I'm playing the Abedju mission (Royal Scribe level), and the Monument rating requirement is 17.
When my medium mastaba was ready, the Monument rating went to 11. Then it dropped to 10.
Now my first small mastaba is also ready, and my Monument rating is 13.
I guess when the second small one is ready, it will be 16. Just one below the requirement.
As far as I know, Monument rating is achieved by building the monuments required and allowed by the level. So there's no way of getting one more Monument point. Does anyone have any idea how my Monument rating dropped by one and how can I recuperate?

That's what I was afraid of... These took so long to build, it'll be a hassle.
Maybe I'll just do the other mission for this level (Behdet) - is there a way to select the other quest for any given level, like in Caesar III?
Will starting Behdet from the "Choose single mission" menu allow me to proceed after winning the map or will it just end and quit to the main menu?

If you took progressive saves, you could've just reloaded from a save point before the monuments were built (aka, the monument footprint).

To select the other mission, you'll have to play in the campaign and finish the mission Timna. If you've taken a save before the Victory screen, you can just reload that and select Behdet. Choosing Behdet from the mission select screen will return you to Main Menu, but Abedju/Behdet are the last missions of the Archaic Period, so it doesn't really matter.

Thanks for the answer.
I did make many progressive saves, but it'll still take way too much (game)time to build the mastabas again.
It's a shame there's no way to select the other mission for the level like in Caesar III... I'll just reload my last save from Timna then.