Replying to myself here in case anyone has the same question in the future: I looked into this more, and I see that there would be an impact if any of the other columns have values for some of the rows but not others -- for example, if a wash sale disallows the loss on a particular row, or if any tax is withheld. But in the instance that all of the sales have the same result (e.g., no wash sales, no tax withholding), my personal understanding (I'm not a tax attorney) is it should be okay mathematically.
I do still have other concerns, though, and created a follow-up post at https://ttlc.intuit.com/community/investments-and-rental-properties/discussion/after-entering-totals....
