“That is something that you sometimes see counties do, correctly, in a primary election,” said Secretary of the Commonwealth Al Schmidt, noting that independent voters can’t participate in Pennsylvania primaries. “It appears that Chester did that pollbook extract and only included major party voters.”

The screw-up meant 75,000 third-party and unaffiliated voters were missing from the books, forcing many to cast provisional ballots. By Thursday, Chester County had collected more than 12,100 of them, a staggering jump from the 843 provisional ballots in 2023 and just 626 in 2021.

Unlike other Pennsylvania counties that use electronic pollbooks, Chester County still relies on old-fashioned paper ones. When the error was discovered early Tuesday, officials scrambled to print and deliver new pollbooks to all 230 precincts — a process that wasn’t completed until 3:45 p.m. A judge later extended voting until 10 p.m. to make up for the delay.

“As far as how and why this happened, that is what we’ll be looking at once all votes have been counted, including the provisional,” county spokesperson Rebecca Brain said Wednesday.

In Allegheny County, election manager David Voye said they perform “spot checks” before printing to ensure both partisan and nonpartisan voters appear from “A to Z.” Chester apparently skipped that step.

Schmidt said Delaware and Philadelphia counties stepped in to supply extra provisional ballot envelopes to help Chester keep up with the rush, since those can’t be printed on demand.

During last year’s presidential election, the county logged just 3,454 provisional ballots, less than a third of this year’s total. Officials say ballot counting will begin Friday morning and continue for 12 hours a day until every vote is processed.