I also sowed some radishes in a big tub last October and just left them in the greenhouse. Never overwintered them before and was expecting them to be quite woody but I was pleasantly surprised.
They did have a slightly woody core but mostly they were perfectly palatable, although lacking in the 'heat' I expect from a radish. Definitely an experiment to repeat next winter, perhaps using several varieties.
I know it's been quite a while since I posted anything. Put it down to the time of year, health problems and appalling weather but the sight of new growth in the garden has me itching for a new start. Just have to remember not to overdo things......not much chance of that, according to my wife!