BGG.CON! BGG.CON SPRING! BGG@SEA!
It's been a few years since I've played, but I believe I'm right with these...
(1) What do you do after you've guessed your numbers?
- Do you start working on a new sheet/diagram of numbers?
- Do you continue working on the one you are currently using?
New sheet. The old information ("I don't have any odd numbers...") is not necessarily accurate. Start a new sheet, and begin by marking out what you KNOW you don't have (e.g. the tiles in opponents' racks and any in the discard pile).
(2) Also what do you do when someone else guesses his/her numbers?
Use same sheet. The information you've gathered so far is still valid, and when an opponent makes a guess, they show you three more tiles that AREN'T on your rack, so you get a chunk of new information.
(3) The used tiles get shuffled back into the back?
You still know what is visible (e.g. opponents' tiles) and the info you've received from opponents still applies ("I don't have any odd tiles"). Start a new sheet with that information. You can't be sure that a newly-revealed tile is truly new, or a duplicate that you've already seen in the discard pile.