Allan Atlas in the article I referred mentions that "Victorian" tutors from Regondi, Blagrove, Sedgwick and Warren prescribed that 4th finger should be used anywhere on the EC keyboard when suitable...Warren later and Alsepti that fingers 1-4 should be used on rows 1-4 respectively i e a fairly frequent use of the 4th finger contrary to the more common routine nowadays that the fourth finger is "resting" at the finger plate.
Seemingly none of these old "greats" presented any analysis WHY they advocated for the "four finger methods".

There is one obvious and very important anatomical reason to choose the fourfinger methods instead of three finger methods however and that is the connective tissue links between tendons of 2nd, 3rd and 4th fingers that makes it impossible for particularly 3rd and 4th finger to move independently from each other. This is a VERY strong argument against using the finger plate at all.William Wheatstone very strongly pointed out in his patent paper of 1861 that the common grip between thumb in the thumb strap and 4th ( AND 3rd! ) finger causes a crampful obstructing fingering situation and due to that he dismissed the finger plate entirely and introduced a support for the wrist or palm of the hand instead to regain stability.

All 8 fingers can be used by Anglo and Duet players. There is no good reason against that with the English either or not to use a similar handle for all concertina systems. The trad set up with thumbstrap combined with little finger rest for the English can be looked upon as an unfortunate historic mistake !