Exploring possibilities is fine, but you have to think about probabilities, too. On one hand, you have the possibility that you've discovered not one, but two previously unknown repunched dates from 1928 (from two different mints!), easily visible on heavily worn coins, but not yet known to other collectors of this hugely popular series. On the other hand, you have the possibility that you're seeing some combination of die chips, damage, or patina disturbances, and as a human being you find it quite easy to interpret them as a familiar pattern. I don't have the coin in hand, I'm not an expert in this series, and I'm not an expert on RPDs (or even die chips), so there's no need for anyone to consider my opinion here. But looking at it from the outside, I know which possibility I would consider to be most probable...
Like the 1919 ddo Mercury dime..... in circulation some 95 years.....and just found and posted here this year!
Im with you paddy, i think the 1st coin very well could be an RPD or possible overdate. The 2nd coin im with the conservative crowd, die gouge or die chip.
Here are some new images after being soaked. The first two are the 1928 s, the following 3 are of the 28 P