Why Are Some Photos Missing From My Takeout?
Usually they are in a different part of the export, or the export was still being built when you downloaded it.
Check the other parts first. Google splits libraries across numbered zips, and a year can be spread over several. Photos also sit in album folders as well as year folders, so a picture may be somewhere you did not look.
If a whole span is genuinely absent, the export may have been built while the library was still syncing, or it may have quietly failed. Requesting a fresh export is the fix.
Takeout JSON Metadata Fixer counts what it finds and reports anything it could not place, so you can tell a missing photo from a misfiled one. It runs on your own computer and is free for your first 500 photos.