Man that Plex Dance is silly and is a result of very lazy coding. Part of what the checksum can consist of is the file size before it goes into the database. Here’s an example -
FileName SHA-CheckSum Size
Name - S00E01 - Trailer.m4v cf0ae9bf1cb661f080e27852d6f4e1a483360084 637504942
Name - S00E01 - Trailer.m4v d87f8a91eb15524f0988a1d8f3ad071e3766b2d5 7712174
I don’t wanna get too technical, but in this example, the second file would be replaced by the first (like if a date comparison is later than the first). The scanner should do it by date if the filenames are the same, not by the checksum. It’s not a true checksum if the date and filesize aren’t generated within the checksum before it goes into the database. I hope that made sense. 
