I don't yet have a clear picture of what situation you are in. From the thread so far we have these descriptions:
- The question banks are still in the site, but the quizzes that were in various topics are all gone.
- The attempts were there. the actuall quizzes themselves were gone from my topics.
- I tried to create a new quiz, but it says I cannot edit it because there are attempts.
- Apparently something is happening with the tests, because when I try to create a new test, and click "save and display" in order to add questions, it tells me there are attempts on the test already (even though I just created it). The numbers of attempts LOOK like old test data. Like the quiz I made this morning said there were 186 attempts. So I deleted it and tried to make a new quiz with a different name and it says 212 attempts. Whene I click on the attempts to try and find and delete them, NOTHING shows up. It looks as though there were no attempts.
- When I click on the attempts and try to search for them, NONE come up.
- I think I might have solved the problem by resetting the course to delete all quiz attempts.
- the number of marks is 61 when there are only 51 questions, all regular multiple choice and all worth only 1 point.
The only thing that could explain this is if the mdl_quiz table got deleted and recreated, or truncated by the person who did your upgrade. Just to be clear, the upgrade does not do this. This is something someone would have to do manually, and there is no good reason why they would do it.
If the mdl_quiz table got deleted, then new quizzes would start being created numbered from 1 again, whereas other data in your database refers to the old quizzes with ids 1, 2, 3, ... So, now, when you create a new quiz, and it gets automatically assigned id 7, say, then any old data that belong to the original quiz with id 7 is now sort-of associated with the new quiz you created, except that it relates to the original quiz, so Moodle can't really understand the data, and that leads to the weird behaviour you see..
To answer you last question: is there any way to undo the upgrade and do it again? Well, if you have a backup from before the upgrade, you can restore the backup, to get your 1.9 site back, and then do the upgrade again. I suggest you do that.