I have a little plastic food tray of leek seedlings.
They have been in the tray since May/June, mainly waterlogged, recently
frozen.
They haven't grown but then again they are still alive and looking as
though they just need planting up to get going.
I'm pretty sure this is not the recommended way of over summering leek
seedlings.

I'd use them as they are, if you plant them out they will just run to
seed in the spring and will have a hard core.