Here in zone 8, put in triple curled parsley plants last year. I had
always considered them to be cool-season annuals, but they grow
surprisingly well here. Kept some going through the winter (they even
seem to be tolerant of mild frost), and planted more this spring. The
difference between the old and new plants is noticeable, though. Old
ones are deeper green but with somewhat more flattened leaves. Taste
is the same, as far as I can tell.

Is there any disadvantage to keeping such plants going through the
winter? That is, does the quality of the leaf continue to change?