Board Thread:General Discussion/@comment-31371445-20170222233857/@comment-31536324-20181227101556

The problem is that, if they could SAVE, then they had to have either had limited uses (which is a rule not even mentioned in the game), never had it (which goes against Toriel's quote), or (as you suggested) lost the ability to use it through losing enough DT to fall below the threshold (which is a possibility expressed in the game, does go with Toriel's quote, and matches up with what we learn in-game).