Have potatoes changed over the years? I've noticed that they seem to be more starchy and repel water content when cooked. Can you please explain this?

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