So.... I was curious to know if ALL P mints were filled in? I found a couple from 1980 and coincidentally, they were both filled.
I think it depends on the die used, also I think that when some of these wear down, the P starts to fill in more.
In my experience, the dies used or the overall quality of the 80's clad coinage was just horrible. There's no premium in my opinion for filled mint marks during this era.
Yup, I just got a few uncirculated sets today to break apart to make my uncirculated series sets I'm putting together, several 1977's had the mint marks filled or nearly filled.