As of 12:36 PM today, I loaded what I think are the last of the records with "smooshed" headings and fields. I say "I think" because 1) it turns out there were a few stragglers I almost missed because mine and Tracy's method of extracting them by call number didn't catch them (invalid call numbers? strange Sudoc numbers? I saved the records and plan on checking or sending a student to check) and 2) it's possible that there are records with smooshed fields that don't fit the criteria we set up when we extracted them.
Even if we missed some, we still managed to touch and fix an amazing number of records in slightly less than two weeks, and almost 24,000 access points that were previously unusable for anything other than keyword searching are now usable as actual headings (i.e., they will now display correctly in browse searches, you have a reasonable chance of finding more items with the same heading when you click on them, etc.). Nice.
My next step will be to start running all kinds of maintenance reports, now that they won't be cluttered up with all of that smooshed junk.