One really slow seedling

[Chucker]

So I'm just curious as I'm fairly new to growing tomatoes.

I started some Bloody Butcher seeds at the beginning of April. They were all started from seeds that I saved from last year. I tried 3 different methods of saving last year and planted some from each trial. All of them are doing fine except one.

I have one seedling that was very slow to come up (about 2 weeks), slow to develop cotyledons, finally just got one tiny true leaf and it's still very small - looks like it's about a week old.

This seed came from a tomato that I let rot at the end of the season last year - and then re-hydrated and extracted the seeds before planting this year.

So, my questions, what causes really slow seedlings? Is it a genetically damaged plant? Did I damage the seed the way I saved it? Does the fact that it was from one of the very last tomatoes of the season have anything to do with it? Will it ever speed up - or should I just give up on it?

Thanks