1. She must have been rich.

Question

2. She cannot have been rich.
3. You should/ought to have come earlier.
4. He may have found the glasses.
5. He might have found the glasses.
(They are all grammatical and talk about the past, right? By the way, what is the difference between #4 and #5?)

6. He will have found the glasses.
7. He shall have found the glases.
8. He can have found the glasses.
(The three sentences are ungrammatical,aren't they? Only 'may' seems to be used with 'have 'p.p.' Is that right?)

Answer 1

6, 7, and 8 are very unconventional! Only 6 is one that might be used.

1-3 are all correct and refer to the past, yes. 4 and 5 have more of the sense of a present perfect (happened and still happening). These are pretty much interchangeable.