You may get the 3%. You are still eligible for payouts but whether old shares get paid out depends on luck.The older they are the more luck would be required to ever pay them (and therefore the less likely they are to get paid).

BTW, luck has been somewhat poor recently which is why you are seeing 97% payouts (sometimes less). I've seen 99%+ at times in the past.

The head start effect is real but the value is very small. It would only matter if you solve another block very quickly (within a few seconds). Most of the time it doesn't matter.