For instance, one has a world where he speedrunned the Eye of Cthulhu. Can he continue from this point for a Night's Edge run?

yeah you can get multiple records in 1 run if you mean it like that

Thank you. By the way, that also means that one will have to to multiple recordings

no you only need to record the run once and you can use the same video to send multiple records

Alright, I got it