Big tick and smiley face for two or three of the groups but I think having to distinguish between the 2 similar groups is a bit harsh, particularly as some of them are rarely seen. The S. versus just S is worth a Google though. Cheers Jahn.

Ditto what BD said- really good grid and interesting about the S. but I'd have struggled with those two even with the full names! I did recognise a lot of them as Pres. mid names but spent most of the time disentangling them from the brilliant Simpsons red herrings! Extremely clever grid, just a bit too hard for me!

Good grid. I got there partly through luck and partly through researching US presidents for a recent grid so I immediately spotted the theme

Cheers guys for the comments.
Can’t believe I missed out the full stop on Harry!
Coincidentally I hadn’t seen DanC’s excellent grid when I did this one.😀

Awfully good, Spiffing fun!