So I was exploring a mineshaft and started to break it apart because I found a spider spawner. I went a couple chunks away and saw a small slime! I turned chunk border on and mined the whole chunk out and started to monitor it to see if they spawn again, several chunks away I catch another slime and make a border for that as well and then a couple more chunks away I find a large slime so I'm confused if I have the slime chunk sizes correct or maybe I found a cluster or a super slime chunk!
More than likely the mobs you put eyes upon didn't actually spawn where you first saw them. Once spawned, unless there's something actively preventing them from doing so (a wall, them being too far away from the nearest player that their AI shuts down, etc) there's really no limit beyond the intrinsic repetitiveness of the RNG to how far away they can wander.
Slime chunks are the same size as any other chunk (16x16). Multiple slime chunks in close proximity are not all that uncommon, so it's possible you did find more than one slime chunk. In my two most recent worlds I have found adjacent slime chunks near my base and turned them into slime farms.
From my older world (started in 1.8).
And a very similar farm from my newer world (started in 1.10.2).
Or it's possible the slimes wandered before you spotted them...
I caught one during it's spawn so I'm positive this one chunk spawns them. The others were too far off to have wandered there and the large slime was in an area too big to get into. So I may have found 4 slime chunks within close proximity to each other. I'm still clearing the locations out so I can section them and run tests.
Slime chunks are random and it is certainly possible to have two or more next to each other, which is not uncommon at all since any given chunk has a 10% chance of being a slime chunk, or, to put it another way, there is about one slime chunk per 50x50 block area:
There are even 6 slime chunks adjacent to each other near the lower-right, and with a bit of searching around I found as many as 10 adjacent slime chunks: