I know this down pretty well by now.
You get all the NPCs by doing seperate things. (Merchant after 50 Silver, Nurse after the heart crystals)
If this is old gen, then you can only get the older NPCs. Any newer ones that came out after 1.3, you can't get.
If this is new gen, you can get all the NPCs that were added onto the console version. This includes newer ones, and older ones. Just nothing after the current version.