Normally numbering in Books starts either with the first page inside, with the first page of toc or with the first page after toc.
You could use sections and define a prefix for the different sections. In German wie use often U1 (Umschlag) for cover page 1, U2 for cover inside, U3 and U4 for the last cover pages, so the prefix would be a simple U. You might use Prefix "Cover " to show it correctly.
Vielen Dank Willi!
I like the Umschlag- idea and the use of separate sections for clean bookkeeping.
Those U- page-numbers are easily converted to (FC), (BC) prior to final commitment to the printer (all I have to do is remember to do so!).
Funny, U-2 brought to mind a rather nasty international incident that took place about 55 y. ago. I remembered names of the principals (Ike, Powers, NK) like it was yesterday.
Often (in my case always) I make the cover as separate file and include both, content and cover into a common book, so that automatic references will work. The cover contains mostly 3 pages (or with the inside 6 pages), facing pages, but with 3 pages each in 2 spreads. The spine's width is changed when selected with the page tool.