There´s not much sense in showing how the results should look, if you don´t tell us from which
patterns you want to start the renaming. Please post "before" & "after" to clarify.
The original files are scans from my negative scanner. The original format is IMG2135.jpg where the IMG remains constant and the next 4 characters increase sequentially. The slides i am scanning are in boxes and they follow the pattern in the first post. Box 10 (B10), row B (RB) then grouped in bunches of 2 (001a, 001b, etc).