Can't date check. Spreads are not exclusive to seeds, seeds are just starting points. Thus it can be far along or in the first few encounters depending on the seed. Some spreads are impossible due to the certain methods of generation, but there aren't many compared to all of the possible spreads.
When the egg is generated, the PID is created and stored. You can change to a later date. Since it can be any date, you can use over 1 million seeds, and thus can get a good egg IV spread out of it. Captures, see above answer.