Nice P2 duo (particularly your LL Duffy).
To me, back condition matters little, as long as the front is well centered (esp P2s), and free of celluloid breaks/cracks, foxing etc.
I view back paper as a bonus -- and depending on the pin (for me), could command a little bit of a premium if it validates content on a unique piece.
I prefer my P2s to have back paper -- but, won't totally lose sleep if they don't.
In your case, both of your P2s look great (IMHO, the rusty collett on the Hooper is fine).
Your Williams is pretty common. As a novice collector, hold onto it -- I love the 1st few buttons I ever bought, even though I can routinely find them on eBay. Gives me a point of reference for how far along my "addiction" has come
