Kuhli Loach Breeding?

I always find it difficult to count my kuhlis as my tank is quite large and well planted, so there's loads of cover. I thought I had 3, but definitely have 4 now. But one is considerably smaller, in body depth it is perhaps a third of the others. It isn't noticeabley shorter in length. Could it have been born in my tank, or could it be a different species that has a different body shape? The kuhlis have been in the tank at least 18 months, possibley 2 1/2 years. Thanks for your suggestions.

I put 5 in, but all about the same time a couple years ago. It's been a very long time since I saw all 5 at once. And I think it's been the best part of a year since I saw 4 at once. I find it really difficult to identify the individual fish, even though I tried to learn their markings, so seeing them together wad the only wayi couldsay for sure how many I have. I have never found any bodies, but as I struggle to find them when they're alive, it isn't surprising. I've heard of people not successfully breeding kuhlis when trying, but finding additional fish. The thing that made me wonder if it has been born in my tank is the distinct difference in size. It is also slightly less timid than the other kuhlis. I know they've been hiding as I've seen the little one a lot more than the other 3, and it is only recently that I saw 3 larger kuhlis at once!