This is only used for Primary election.

为什么要这样子，只要动动脑筋就明白了。

传播这种谣言的人，不是蠢就是坏。

these identifiers are not found on mail-in ballots for the general election, but for primary elections that require prior party registration.

https://www.reuters.com/article/uk-fact-check-party-not-on-gen-election/fact-check-party-affiliation-on-mail-in-ballots-only-for-florida-primaries-not-general-election-idUSKBN25M1TN