10 Lug's RK with 4-hole bridges and vertical knurled tone control knob would likely be '37-'38 per Slingerland historian Dr. Wenk. Note 6-hole bridges appear '37-'38 indicating the exact transition date is unknown or both 4-hole and 6-hole were in use for '37 and '38...
'40-'41 makes sense for levelpeeble's RK. Slingerland historian Dr. Carl Wenk states '40 for first year of tin snare straps and '41 the last year for adjustable bridges.
The British Imperial Unit inch and American inch are the same. Was Premier making "fractionally" sized shells rather than in full inches (e.g. 11-7/8" instead of 12", 16-5/16" instead of 16") or were they using the metric system (e.g. 30cm, 41cm)?
If you look closely at the original badge picture you can make out the second line of text at the bottom that does not appear on the Niles badges ("assembled in"). I concur with you, it is not obvious.
glaze148, the main differences between a Shelbyville and a Niles drum are the oak re-rings and maroon badge on the Shelbyvilles. Primarily collectible to some for being unique rather than somehow better.
+1 with Rich K. "Late '71-early '72, mostly '72" per Slingerland historian Dr. Wenk. Also, "No badges on toms till June '66". While it may seem that badges were positioned randomly, I believe there are rules, we just don't fully understand them.