Very Old New Potatoes

Helped D2 tidy up her garden today. This included emptying her potato barrel and guess what we found in the earth as we tipped it up? Enough potatoes left over for a couple of good meals. The were very solid and fresh looking, defiantly a tasty find.
It raised a question in my mind. These potatoes should have been harvested last July/August and still look good 8/9 months later. If I plant up a potato barrel, grow them as normal but do not harvest them all, would I be able to dig up new potatoes for Christmas dinner? Sounds too good to be true. Anyone out there got any thoughts?