Doesn’t make sense to me. It’s definitely possible to end up with a partial season of VHS tapes or DVDs. Maybe your kid broke a few. Maybe you loaned part of the series to a friend and they lost it. Maybe your collection is tapes recorded off the air in whatever random order they were rebroadcast during syndication.
The library feature shouldn’t tell us how we can collect media. It should reflect reality, no matter how weird it might seem to the system architect.