Some time ago you resolved issue 55595 so that when a mailmerge is done, the
page number/page count is done per record, not for the entire document.

Although this is great for printing bulk letters (each letter has its own
numbering), it makes impossible to use page number/page count for other usages,
such as editing catalogs.

Say I have a list of 500 articles, and I want to create a liste of them, 10
articles per page. I can use mailmerge for that, and I get a nice 50-page
document. Now if I want to work with colleagues on that list, I definitely will
need a consistant page numbering (1/50, 2/50...50/50). But mailmerge cannot do that.

So I suggest that the service MailMerge would be enhanced with an additional
property (let's call it GlobalNumbering for now), that would default to False.
When set to True, it disables the tricks introduced by issue 55595 (1 page style
per iteration of the source document, if I'm not mistaking), and maybe it skips
the insertion of empty pages (if necessary for a valid page count).

On the UI side, well let's say that the mailing assistant was written from a
send-many-letters point of view, so it's not very well adapted for the case I
describe here. One could start with a checkbox option somewhere, keeping in mind
that a rewriting of that assistant could be a good idea (okay I don't like the
mailing assistant, but please note how carefully I try not no start a flamewar).