Yep, if you add up all the straight party line votes and the presidential votes you get to 1,260,350 vs. 1,139,074, that might be due to people posting both straight party tickets and presidential votes I guess, but if you go into the Detroit only figures they have. 497,045 total ballots cast vs. 446,523 votes cast for President which doesnt match with that explanation. Also Detroit has 511,786 registered voters vs. 497,045 ballots cast. That’s a 97% turnout. That along with the Free Press story about not being able to match ballots to votes cast piqued by analytical nature.
I think you’re misreading the report. Straight party line votes are a subset of the total number of votes for president, not every vote for president was part of a straight party line vote.
If someone votes straight party line and also marks in for president separately the individual is counted. Once.