As far as I know it has remained the same since 1964 with the exception of the Bicentennial coins ('75-'76)......
If you look at the back the little round balls went from being round and smooth to round with what looks like a nail imprint. Looks like this happened sometime in the 80s maybe?
I hope so lol. I thought I was seeing things but every one I’ve looked at at least before 83 has round smooth circles. All after appear to have a nail imprint. I can’t find any information what so ever about it. It seems like no one noticed ?
I'm sure there are many that did, but an old dog like me lets' many things escape the senses..........
The circles represent Clouds in the "Glory Or" Or Halo of Gold. The indents that you asked about have always been on the Kennedy Half. Early years are not so pronounced as the later ones. Look at one of your 1964's and you should see what looks like a Half-Heart attempt to engrave them on some of the circles. Remember this design was rushed along in its first years. I think it just took them a long time to refine it. Some info here. https://www.whitehousegifts.com/pages/the-presidential-seal-a-brief-history
To help here with Alurids statement. Earlier die states showed definition in those areas. As the die wears, the strike quality goes down, most of the fine details are lost by Mid die state.
