Having worked on TV & Radio sets for more than a few years, I can say from my own experiences:
Sam's- Especially the early ones did have a lot of misprints in their schematics. They did put out correction notices, but you had to be subscribed to the POM club to get them in your monthly box of schematics. Good format layout. They combined Radio & TV into each folder, and often some odds & ends. They eventually came out with a series of HTP- Home tape Player, AR- Auto Radio, MHF- Modular Hi-Fi, Communications Receivers, TR- Tape Recorder, T/T- Turn Table, SD- Scanner Data, & VCR to the best of my recollection. They may have had a couple of more series. If I remember more, I will post them.
OEM- Typically they were much more reliable in accuracy. The mfg. would send out updated service manuals to their Factory Authorized Repair Centers with the latest mods, problems, and repair solutions. They would also mail out updates, and "U paste it" service notes to add to existing manuals.
TAB: Published brand specific books of schematics- which may or may not have been terribly accurate, due to lots of typos at times. They had a series of Japanese TV books that were helpful, but not really comprehensive. B&W and Color sets
Cissins (sp) : Basically copies of OEM data--BUT they had schematics no one else had. Mostly dated back to the B&W days.
Beitmans: No training manuals ,but had different sets for Radios, TV, and I think some others. Not dense coverage, but again, they had some schematics others didn't cover.
Riders- Radio & TV manuals: They had updates and pretty good accuracy in both Radio & TV manuals. In addition they made a PA series, and included training manuals in most of the volumes for Radio. (I can't remember if they did this for the TV set). Mostly Radio & B&W TV. IIRC, they did publish a few on early color, and transistor radios. (The transistor ones I saw were in a TV binder.) They published 23 vol. for Radio and 28 (?) on TV. Vol 23 of radio is the hardest to find. (Some folks have scanned the Radio onto disk and the whole set sells cheaply, but there are some very poorly scanned sets out there. Beware!)
Additionally, the mfgr's would send out training materials.
Zenith Sight & Sound: Tapes and schematics, in later years video tapes and CD 's. Not too bad, all in all. Great factory tech support.
Later Zenith became LG Zenith, then finally LG. Still had good tech support till I retired. They would help out ANY service center. Kudos to them.
Hitachi: Killer training aids, and the BEST tech support in the industry until Walt Herron left, Then meah... Still had support, just nowhere as good.
RCA: Killer training manuals- probably the best I ever saw. Very detailed and thorough.
They also sent out VCR tapes and CD's
Magnavox/ Sylvania/ Crosley/ NAP/ PCE: Training manuals & tapes. (Note: I thought the tapes pretty much worthless. I never ran into a single problem that the training tapes covered, and they mostly were the same format and cures, as most of the circuits were a rehash of previous ones, just different chassis. (IE: No power- Open diode in power supply. Really basic stuff). The training manuals were pretty good though.
I'll add more to this list as time goes by & I remember my experiences.