Kennedy Half 1982-1989 P And D Mint Marks And Red Book Value

Hello Coin Community,

So after going through a box of halfs I kept everything in red book(2020) that had a value of 4 or more. This is at MS 63 of course and I am not well versed in grading. But have two questions:

Why are they valued more in Red Book is it because the mint had poor quality during that time and MS63+ are hard to come by? Or are their other reasons.

So I have manly the 1983p but also many - 89 no 87's unfortunately in the find.

Here a pic of one of the nicer 1983Ps I rate it as just under AU45/50 maybe less. And If they are worth nothing at that level and considering the mintage what waste pace and money holding them.

Thanks,
Dyno