I normally get the AC/Delco filters on sale at a local farm store called Rural King when they are on sale for 2/$7.00.
Over the summer... I havent seen them in the sale circular... so I just picked one up at WM with my Supertech synthetic... & noted the change in part #.
I get the feeling that with corporate mergers... all filters except the premium brands... may come down the same line in different batches... & I bet that you are correct about the base plate being a common part sourced overseas & fitted with the different dimension threaded fittings for various applications.
05 Z85 crew cab 4x4 - SBM
235/75-15 BFG A/T KO / Firestone Winterforce 235/75-15
WM Super Tech synthetic 5w30 & AC/Delco PF-61
Duralast brake pads & shoes
GM contour splash guards
AVS Bugflector II
DecalKing Z85 & CF
08 Buell Blast
11 Ford Focus SE
Gun Toting American Club Member #4