To meet higher USDA grades, it seems like they must be pre-sorted to remove mold (among other things).

Example: https://www.ams.usda.gov/grades-standards/frozen-strawberrie...

PS: Side note, either USDA AMS hasn't updated their site in awhile, or some "most recent" frozen berry standards date back to the 50s/60s. Which, I guess makes sense; I imagine the process hasn't changed that much.