I still can't see where that has anything whatever to do with loading mags with loose rounds in the field.
Here in parts of Utah, you can find the same manning tables today.
Troopers & deputies can expect backup to arrive in 10 minutes or an hour, depending on their location in some areas.
They carry reloads, in mags, but not loose in pockets or cars.
I can see no good reason whatever for dis-allowing mag loaders at the range. Easier on the fingers, speeds up reloading times between strings.
Has zero effect on field use of the duty weapon.
As far as round counting goes, that was demonstrated to be so far removed from the realities of a dynamic shooting encounter that it began to be dropped by knowledgeable trainers well over three decades ago. My department & nationally ranked instructors outside it were avoiding it in the early 80s. May have taken some time to spread, but I haven't even heard the term used in many years till you brought it up here.
It's the reason more effective training has replaced it. That consists of basically if you fired anything at all, you reload at the first opportunity. Studies & de-briefings have shown clearly that the various sensory input processing in such situations is so distorted that most could not accurately recall how many rounds they'd fired, and later were very surprised to hear the actual number.
There are so many other things going on that trying to count your rounds fired is very counterproductive, to say the least.
Denis