I believe most of the patches for New Leaf were bug fixes until the Welcome amiibo Update which was 1.5 brought new features and was pretty much the last update.
But can't find any official history.
Yea the welcome amiibo update was the main big one in New Leaf. I believe they released special items throughout the years with different regions getting different items. You could check the internet for it at I believe the post office but eventually they stopped putting those special limited items out. Welcome amiibo update was pretty decent though since added more items, camp area for new character Harv and 2 mini games that were semi decent.