Encyclopedias and Dictionaries and General Reference Books That Discuss Prem Rawat(ism)
Encyclopedias and Dictionaries of Religion would be the places an interested person might consider that authorative, though condensed, information would be found on Prem Rawat, Élan Vital or Divine Light Mission. I have collected various texts but found their error rate quite high.

Abingdon Dictionary of Living Religions
Crim, Keith R., Shinn, Larry D., Bullard, Roger Aubrey
1981
A very concise and short entry that reflects Divine Light Mission's small size and minor importance but they certainly capture the essence of the religion: "The American organization of the GURU Maharaj Ji (b. 1958). His followers consider him an embodiment of God, and the essential fact of life is their relationship to him"
Encyclopedic Handbook of Cults in America
J. Gordon Melton
1986
Revised Version, 1992
Neither of the egregious spelling errors in the Élan Vital entry have been corrected in the 1998??? revised edition. While Melton is considered the doyen of "dictionarisation" of religions, his objectivity has been suspect, especially since he and James R. Lewis raced to Tokyo to defend the AUM cult (at the cult's expense) from charges of releasing poison gas in the Tokyo subways. He is, after all, an author who calls the mass suicide and murders in Jonestown, Guyana in 1978, an "incident".
Religious Leaders of America
J. Gordon Melton
1991
Melton has corrected the spelling of 'Dulga' to 'Durga' in the 'Guru Maharaj Ji' entry which is a shortened version of that in the Encyclopedic Handbook of Cults in America.
Who's Who Of World Religions
Editor John R. Hinnells
1991
This is a pretty standard short version of the Divine Light Mission saga of the 1970's, with the usual mistakes taken from the Encyclopedic Handbook of Cults in America.
Contemporary Religions: A World Guide
Edited by Ian Harris, Stuart Mews, Paul Morris & John Shepherd
1992
A short, concise entry that provides some interesting information but unfortunately it contains some obsolete data without attributing it to it's period.
An Encyclopedia of Religions in the United States
One Hundred Religious Groups Speak For Themselves
edited by William B. Williamson
352 pages, Crossroad Publishing Company (January 1992)
It's like asking the residents of an insane asylum to diagnose themselves.

Dictionary of Cults, Sects, Religions and the Occult
Rev. George Mather and Rev. Larry A. Nichols
1993
A long and quite accurate account of DLM and Prem Rawat. It is written from a Christian viewpoint and it's use of Christian terminology gives an interesting perspective on Rawat's teachings. Rawat has made his teachings simpler and less specific over the last 30 years but Mather and Nichols' doctrinal definitions were taught by Rawat at one time and have never been renounced.
Religious Bodies in Australia: A Comprehensive Guide
Rowland Ward and Robert Humphries
431 pages, New Melbourne Press; 3rd edition (1995)
Short but accurate description of Élan Vital doctrines. Accurately places the peak active membership at 1,200 (circa 1979) and gives the astonishing detail that in 1991, nearly 10 years after it's disbanding, about 30 persons identified themselves as adherents of the Divine Light Mission in the Australian census.
A New Dictionary of Religions
Editor John R. Hinnells
1995
A very concise and short entry that reflects Élan Vital's small size and minor importance.
The Encyclopedia of American Religious History
Edward L. Queen II, Stephen R. Prothero and Gardiner H. Shattuck Jr
1200 pages, Facts on File (1996?)
Has an introduction to Hinduism in the USA which mentions Rawat: "The "boy guru" Maharaj-ji came to America in 1970 and brought his "lovers of God" into the Divine Light Mission (later Élan Vital)."
The Oxford Dictionary Of World Religions
Edited by John Bowker
Oxford University Press (1997)
Accurately depicts the salient points of Rawat's teachings: Religious movement founded by Sri Hans Ji Maharaj in 1960. When he died in 1966, his son (8 years old) is reported to have said to the mourners, 'You who have been deceived by *maya (illusion): Maharaj Ji is here in your midst: Recognize him, worship him and obey him.'

The Encyclopedia of Christianity
Eerdmans Brills (1999)
The movement was largely run by his mother, Mata Ji, until a schism, with Maharaji renaming his part of the movement Élan Vital. Central to the movement's teachings is a belief that *Buddha, "Krsna, *Christ, *Muhammad, and a number of lesser masters have taught what is termed the Knowledge, which consists essentially of techniques of *meditation. This Knowledge is transmitted from one master to another, each one being the only perfect or true teacher, satguru, during his lifetime. Followers or 'premies' believe that Guru Maharaj Ji is the present satguru.
The Encyclopedia of Hinduism
Constance A. Jones and James D. Ryan
552 pages, Checkmark Books (October 30, 2007)
Uncritically repeats the Élan Vital approved version of Prem Rawat's career.

The Encyclopedia of CULTS, SECTS And NewReligions
James R. Lewis
2001
This is mainly an abbreviation of Encyclopedic Handbook of Cults in America by the doyen of NRM apologists.

CULTS (Contemporary World Issues
James R. Lewis
2005
This is mainly an abbreviation of and updating of The Encyclopedia of CULTS, SECTS And NewReligions by Lewis, still the doyen of NRM apologists.

A Brief Guide to Beliefs
Linda Edwards
592 pages
Publisher: Westminster John Knox Press; 1st edition (January 1, 2001)
Chapter 8
UNIT 8:1 ELAN VITAL (THE DIVINE LIGHT MISSION)
Uncritically repeats the Élan Vital approved version of Prem Rawat's career and the "Siddha yoga" error found in Mather.

An Encyclopedia of Claims, Frauds, and Hoaxes of the Occult and Supernatural
James Randi Educational Foundation
A mainly humorous look at Rawat's career "highlights" with one major mistake, Rawat appeared at the 1971 Glastonbury festival, not in 1981.
The mission had as its membership mostly middle-class young people, who were taught that rational thought is the supreme enemy and were urged to immediately commence meditation whenever the thinking process threatened to return. The Maharaj Ji announced that the "most significant event in the history of humanity" would take place, "Millennium '73," at the Houston Astrodome. The arena was rented at a frightening price and admission was free, but only twenty thousand of the expected sixty thousand persons showed up. It was a bust, especially financially.
The Historical Dictionary Of New Religious Movements
George D. Chryssides
2001
Apart from the repetition of the claim that Rawat denied "both his divine status and status as a guru" for which there is no evidence and some some strange wording that sounds like it was written by Élan Vital spin doctors and seems to accept that his teachings actually can "afford self-understanding and self-realization", it is reasonably accurate while leaning to every possible positive spin on Prem Rawat and his religion.
Religions of the World
J. Gordon Melton
1991
The A to Z of New Religious Movements
George D. Chryssides
2007
Anyone reading this book would not learn that any new religions movements had ever been involved in controversy unless they were unfairly accused by members of the disreputable anti-cult movement. However, apart from the repetition of the claim that Rawat denied "both his divine status and status as a guru" for which there is no evidence and some some stange wording that seems to accept that his teachings "afford self-understanding and self-realization", it is reasonably accurate while leaning to every possible positive spin on Prem Rawat and his religion.
Chambers Dictionary Of Beliefs And Religions
Edited By Mark Vernon
2009
Chambers Harrap Publishers Ltd
Short and accurate entry.
United States Army Requirements and Practices Manual
An official document from 1975
Encyclopedia of New Religion Movements
Peter B. Clarke
Encyclopedia of American Religions. Melton, J. Gordon. 1996. Detroit, MI: Gale. Fifth Edition. "Divine Light Mission" pp. 890-891.
Encyclopedia of Occultism & Parapsycology: 4th Edition. Melton, J. Gordon. 1996. Gale. "Maharaj Ji, Guru" pp.803.