I have a resident permit of Schengen country X.
I entered Schengen directly from X with stamp from X.
I take a bus to another Schengen country and leave Schengen from there without a stamp.
I come back to X from a Schengen country that doesn't stamp.
There are no other stamps on the passport for that period.
Will X know I was not in the country? They would know if they really want to know but I'm talking about normal circumstances. Asking for residence permit renewal and citizenship application.