Can I check, when BBC says how many votes are left to count, does that include mail in votes?
Like so many things, this depends on the state. Some count absentee votes first, others count them second (just as some states require them to arrive before the election and some give a grace period of a few days and still be willing to count them).
In PA, to my knowledge, yes the mail-in votes are counted second and it was expected for them to not get to them until this morning. I think this is also true in Wisconsin, Michigan and Georgia.