Rest assured that potatoes have not changed, generally speaking over the years. What does happen is a new crop potato (freshly harvested) will vary somewhat, compared to the tuber which has been held in winter storage. As potatoes go into their dormant stage for long-term storage, they dehydrate ever so slightly as the weeks and months go on (but not appreciably). However, this does diminish the water content so the solids/starch component of the potato will naturally be a little higher than when first harvested. The other factor is temperature. You should keep your potatoes stored cool (but not cold) no colder than about 42°F for too long – as the starches convert to sugar and this will change the cooking chemistry.

Here’s a link on the proper way to store potatoes: proper way to store potatoes