I would have thought that there was little to be gained by planting them in the pots as the increasing size of the tubers would be a little starved of water and space. You have several options. You could plant them direct in the ground and left them to overwinter if your soil was free-draining and a little mulch on top to protect them. You can wait until they have died down and lifted and stored them as you have most probably done last year. But I would have lifted them, stored them overwinter, started them off in pots or trays with a moist compost and taken cuttings to produce lots of new plants.

Many thanks for your advice. Although we have free draining soil, I think we will lift them and have the opportunity to split them in the Spring.

Welcome to GOY. Dahlias are a strange plant, some will over-winter quite happily and other disappear! I have done both, most years I have dug them up, knocked most of the soil off (carefully) and stored them somewhere frost free, only to find frost-free doesn't mean mouse free! Last year they got left in the ground and our ground is solid clay, retains water and sets rock hard in the dry! However as it was a mild winter they came through quite happily and are miles ahead of where they usually are at this time. Take care if you talk about splitting them, they need a bit of the stalk/crown, not just one of the tubers - I think!!

Honeysuckle, you're dead right. You can't just divide them, they need to have a piece of the stalk/crown, best to take cuttings.

I always sink their pots into the ground and lift them in the autumn. saves damaging the tubers and my back!
if they are larger they get a larger pot next spring.