Hi Dave the tubers will have rotted away by next year, even now they should have eyes, or sprouts, on them these will use the tuber to grow. Wouldn't recommend reusing the compost for potatoes but will be fine for anything but solanums.

MG why solanums please, and what to use instead? (I'm not thinking of potatoes but the little ones with orange berries that are sold around Christmas.
(Sorry Dave for muscling in on your question - why not try putting your surplus potatoes on Freecycle - somebody might be glad of them)

They are all part of the same family… so doing plant/grow in the same place two years running Stera.

They live in a pot indoors MG! I was wondering if they reason they don't seem to flourish is because they are in multipurpose.

I doubt it is the multi purpose compost Stera more likely the way they are looked after prior to being sold in the GCs and supermarkets. I remember seeing some in an outdoor Christmas market looking wonderful - Bulba pointed out that having been outside in the frost and snow they were less than likely to survive in our house.

Can't blame the shop but as the months go by they just begin to look tired and after a year or two tend to give up.
I suspect they need more water and food than they get!
I put them outside for the summer and they seemed much happier there but the three or four year old one gave up this spring..