Yes, it is a known problems - there are litterally many hundreds of thousands of buildings missing in Croatia alone.  As this is volunteer run project, you can add them in places which are of interest to you.

So, unless the rest of the area is fully mapped and only a few (i.e. new developments) buildings are missing, there is no need to leave Notes about missing buildings -- we know.

I've now added dozens of buildings missing at that particular spot, but many more missing even in just this village.