I think most do not gain more spots but some do change with maturity. Whether their spots fuse or difuse into more, they all have potential to change. Mine is gaining more spots along its dorsal/back, and they was no evidence of them when it was smaller. I've had lots of knives and this is a first. It's the one in my avatar.
I just noticed a few more really faint ones. He must of been stressed really bad before cause even the 4 main spots were faded, now there really dark. CK's are awesome!!!
I've experienced growing up Clown that didn't get any spot!!! In my count, 6... It really disappoint me and end-up selling them in cheaper price... But I have 2 clowns now and they really do have very many spots... If you want knife fish with very many spots, get some Emperor knife...
I have a Clown Knife that grew 1 to 2 more spots within the last 5" of growth( it's about 8" now). I say "1 to 2", because my CF started out with 11 spots on both side off it's body, but now has 13 spots on the right side and 12 on the left. I don't know if he'll grow more. I can only relay what i've seen.
i think they gain spots as they grow, because i use to have a huge clown knife, held it in a 55g before i sold it, it was about a foot long. and it had alot of spots, more than any of the small ones sold in stores.