Nope, you need more than 1 subscription, because quite often services only offer a few of the seasons of your favorite show, while the others are on different services.
Example: https://www.pokemon.com/us/animation/where-to-watch-pokemon-episodes-movies
Maybe is in the metadata as someone pointed out earlier, or it could be an otherwise unused ASCII char that looks different for each user who licensed it when printed out, sort of like a qr code as a single ASCII char.
Or it could be that they simply just check filename, file size and/or md5, all of which can be easily changed.