We at Tiswas Online are researching every single episode of Tiswas, which region showed it and who was on it. The episode guide on the website is the most comprehensive ever attempted on the show:
http://www.tiswasonline.com/episode_guide.php
For regional variations, you need to look at this thread on our forum:
http://www.tiswasonline.com/forums/viewtopic.php?p=6460&highlight=regional&sid=1dd36fc6a789934ca5fa8cac75f77c5e#6460
(probably need to cut and paste that link)
It's all very much a work in progress and contains information from many sources:

The official ATV archives,

Our own video copies (many more than exist in the archive - although ITV are fully aware of this and we work with them quite often).

Scans of *all* the original TV Times listings

A fan who meticulously noted every item in almost every show of the original run.
...and much more...
We're working closely with the production team of the new show on many aspects...
One last thing, you may not always find Tiswas listed by that name, it's original listed was "Today Is Saturday or The Tis-Was Show", the titles showed "Today Is Saturday" followed by the original chunky-lettered Tiswas logo. The first programme aired on ATV on 5th January 1974 (having been piloted in a different form by Peter Tomlinson during the previous summer).