You'll need to update your documents with immigration when extending your stay in Thailand. So far, when crossing the border, it seems the vast majority of people don’t need to show anything. However, balance your risk as immigration has full authority to perform checks at any time (and remember what are their conditions for extension). Don’t rely on those who claim that checks will be "announced" that’s pure nonsense. Checks have already been conducted on other types of visas (student, volunteer, etc.). My best advice is to check visa forums where long-term expats share real experiences with immigration.

The government doesn't need to notify you before checking its borders and if visa holders are fulfilling their visa requirements. Did they warn all the ED visa guys who got caught at some point? Sorry but you don't hold a special immunity with the DTV visa.