Once again, you won't find it in handbooks because the handbooks were printed before the storyline took place as was pointed out previously.
However it's written into several characters bios on marvel.com and marvunapp. Marvunapp being where 'official changes to the handbook' are made, and the paper books even reference the site as the source for additional information in every one of the latest handbooks in 05-06
As such it's referenced here in the Wing Thing's bio of significant issues. A character from MC2
http://marvel.com/universe/OHOTMU:Bibliography-AZ12#Vegas
Referenced here again in an update to the ohotmu on Marvel's site.
http://marvel.com/universe/OHOTMU:Bibliography-AZ_Update_1
http://marvel.com/universe/Sabreclaw here again as a signifcant issue in Sabreclaws bio.
http://www.marvunapp.com/Appendix4/argoalmightymc2.htm Here in Argo the Mighty's bio on marvunapp.
http://www.marvunapp.com/Appendix4/sylenemc2.htm
Here in Sylene's bio on marvunapp.
Even Mr Master recognizes this;
Originally posted by Mr Master
(excerpt from the Official Marvel Handbook 2006)
[B]"The LT has NO Counter-Parts ... ONLY ONE LT exists in the Multiverse"LT is the Judge of ALL Realities in the Omniverse, and can exist simultaneously in all:
"The LT Exists in ALL Multiverses simultaneously"
The Full Sentience and Power of LT resides within any M-body he wishes to manifest, there is absolutely NO On Panel or Bio evidence proving M-bodies come in various levels of Sentience or Power.
There is only proof that M-bodies come with the Full Power of the Concept.
http://www.marvunapp.com/Appendix/anthropo.htm
This Site is Officially sponsored by Marvel[B] in every single Handbook 05' & 06'.
Pretty much to sum it up, it can't be canon for everyone involved -except- the Living Tribunal. There is only one. Living Tribunal's bio shows a lot of alternate universe and 'What If" appearances already.