Concern about PA

I'm not concern about PA polling, Joe is doing fine there.

However, I am concern about the mail in ballot returns.

According to https://electproject.github.io/Early-Vote-2020G/PA.html

Democrats requested 1,825,586 ballot and so far return 847,350, so a 46%

My main concern is most of the ballots unaccounted for are in the Philly suburb area.
As of 10/21,
Bucks county return just 7.3% ballots.
Delaware county return just 14% ballots.
Montgomery county return just 29.9% ballots.

These are some of the lowest throughout the state and are democratic counties that Biden needs to win.

Are these returns just slow to tabulate or are voters not receiving and/or returning their ballots?

If you request an absentee or mail-in ballot, that request will be reflected in the records of your local polling location. If you change your mind or misplace the ballot and decide to vote in person, you will be required to vote with a provisional ballot. Within 7 days after the election, the County Election Office will decide whether you were eligible to vote at the election district where you voted the provisional ballot. If you were eligible, they will count your provisional ballot.... and if the voting differential is close enough to matter.

In short, if you don't return your mail in ballot, your vote may not count!
In Addition, history has slow, voting via provisional ballot slows poll workers time and possibly increase voters wait times at those locations on election day. There could be a limit on provisional ballots too.

Please relieve me from my concern.