According to the Numista rules for referees, all readable symbols are obliged to be described in the "Lettering" section.
It means, that if there is "Lettering" section in an article (it is in this one) the symbols PM should be mentioned in it. As for the other side of this particular coin there are other readable symbols and they must be described as well in the already existed "lettering" section. This rule solves most of the involved tasks.
Despite of that it is a sign of politeness to a reader to describe the position of symbols, which are mentioned in the year distribution section. This is especially important in case if the catalog encourages readers to contribute unpublished yet information. There are cases, when the photo is of one coin, which has symbols in one place, but there are other coins in the same article, where the place of these symbols is different. The section "comments" I believe is ready to accept a description of all these peculiarities.
For it is the catalog, and not a collection of gossip, it will be perfect to see in the article the facts only. It means, that it is OK if necessary to describe that
these coins are known with die letters: ...
Full stop.
No further suggestion or speculation. If you prefer, may add something similar to a note in the Pick catalog:
Readers with unlisted dates, mint marks, die letters etc. are invited to submit their coins to
https://en.numista.com/forum/topic55214.html ( this is an example, connect to a link at the forum, created for this purpose, or already existed general one).
As for the 40 members whose coin position should be moved, the Numista Catalog faced such problems constantly, and it successfully solved them in Norway 2 ore and many other cases.
As for the hiding the symbols in the Isle of Man section you are completely right, it looks inconsistent, that in the Great Britain part of the catalog , where there are die letters reader finds the information about them and their position on a coin in hands in any article, where they are mentioned (I sent sample links to the Isle of Man referee in private message), in France section and most others of the Numista catalog every readable symbol and its absence is described properly, but in these regional coins section this information is still not available. Reader of the Isle of Man articles gets from the year distribution section that his coin has not just such year but these and these symbols as well. Still he has to solve riddle, where on his coin he has to look for these small symbols.