The following is based on my analysis of documents on http://www.majesticdocuments.com and those that are part of the public domain care of the National Archives and other official sources…

The first thing to point out is there's not a single truly authenticated document that contains references to both MJ-12 and Majestic. This is problematic, because only the unauthenticated documents allege a connection between these two terms.

"MJ-12" shows up on a July 1954 memo from Robert Cutler to General Twining explaining a change of dates for a National Security Council Special Studies Project. This could be anything.

http://209.132.68.98/authentication/archives/pdf/cutler_twining.pdf

"Majestic" shows up in the "Report By The Joint Logistics Plans Committee". This is often given as evidence for a Majestic 12 conspiracy and also that such a conspiracy was highly developed and included plans for psychological warfare. This theory can be completely debunked...

http://209.132.68.98/authentication/archives/pdf/jointlogisticplan_majestic.pdf

Beginning as early as 1948 the Joint Chiefs of Staff were preparing war plans for World War 3. This included the possibility of a U.S. first strike. Originally this was called a Joint Short-Term Emergency War Plan. The first known codename in May 1948 was "Halfmoon" and was simply a target list to drop 50 nuclear bombs on 20 select target centers in the Soviet Union. In August this was altered for budgetary reasons and renamed "Fleetwood". In December of the same year the target package was expanded to 70 target centers with 133 weapons to be used and was renamed "Trojan". By February the Joint Emergency War Plan had expanded considerably under the codename "Offtackle" and now included preparations for a post-strike defense of Western Europe.

Now, there is a space of a few years where I can't find any codenames, but the aforementioned authentic "Majestic" document reads: "Forwarded herewith is a copy of the Joint Outline Emergency War Plan for a War Beginning 1 July 1952 MAJESTIC. This plan supersedes Joint Outline Emergency War Plan MASTHEAD, which was forwarded (...) 14 May 1951.” Majestic war plans called for highly developed WWIII scenarios with psyops, specops, cover & deception, military government, command & communications, logistics & transportation, and mapping & charts. As should be obvious, it is a logical conclusion for the early war plans to have evolved to this point. Thus, it can be determined that the connection between MJ-12 and Majestic is unfounded. Yet, the complete Majestic 12 theory essentially has no other authentic documents to support it. Every document that is supposedly proof of a connection is of a completely unknown authenticity.

In addition, there are several allegations that "MAJCOM", which appears on several known authentic documents is also evidence of MJ-12, Majestic, and Majestic 12. In fact, this stands for “Major Command” and is used to this day to refer to major regional military command bases, such as when saying “Forward copy of this document to MAJCOM.” Also, neither “MAJI”, "MAJI CONTROL", nor “MAJIC” is found on a single authenticated document, let alone one also with "MJ-12" or "Majestic" on it. The only place "MAJI" appears is on the questionable documents, such as the supposed Majestic-12 Group Special Operations Manual.

http://209.132.68.98/documents/pdf/som101_part1.pdf

Thus, I must assume the Majestic-12 unauthenticated connecting documents are most likely forgeries.