Lets say everyone in has a deck that has a bunch of the same cards on their anki software, if they subscribed to a deck that potentially had some of those cards that they already have, how does Ankihub handle this instance?
Not sure if I 100% understand your question but to my understanding, this is how it handles them
When you create a new card, it gets assigned a note ID of for example 282189314971
If you subscribe to a deck that has the same note ID of a card of 282189314971, ankihub will update that one (this is how people update from v11 to v12)
However, if you made a card that says “I love Anki” and you subscribe to a deck that has the same card “I love Anki” but the note ID’s differ. Then AnkiHub does not treat that as a duplicate. You would have to manually delete it. Having the same note ID’s by chance is very rare, so unless you manually change it, it wont happen
TLDR: AnkiHub cannot recognize duplicates, unless those cards have the exact same note IDs (based on my understanding)