I can't really say an year for sure. There have been great drums from almost any of the years. Currently I play a 22,13,16 classic maple set and it sounds absolutely awesome. I love the WFL drums too but my only complaint about 50's WFL drums is the rail. I don't care for the two bolt rail and I hate the spot it was put on 50's WFL's. The 60's 4 bolt rail is much better IMO and the positioning is perfect.
I also hear people complain about "Ringo era" drums but I have only really had one bad apple out of many sets. It's funny too because it was a 1966 champagne sparkle down beat in the most pristine amazing champagne sparkle wrap ever and if you looked at the lugs they were all drilled crooked.(Go figure!) I could never get it to tune right.
If the wrap was trashed or it had extra holes it probably would have sounded amazing! Lol...
Every other set I have had has been awesome though and I have had many over the years.