Recast is the exact copy of someone other's work. It's not that hard to tell, I mean we don't have a 3D Scan or something, so you might get close to the on screen armor by sculpting your own molds but it will never be exactly the same unless you cast it from an original armor. RS and CfO did that and if you compare their kits to others You will see lots of tiny differences. (For example that one of the abdomen buttons on the RS has a different size...)
These are only nuances, but if you're into the materia, you'll recognize it. So if somehow another kit hits the market and has this exact one smaller button on the belly - I'd say it's at least suspicious But if you only use another's armor for size reference - I guess it's fine. As long as you don't copy his work.