I did not say that I am 100% sure that the PUC for the BD-P4600 can control the BD-P3600.
What I said and showed was that the earlier P1200 and the P3600 use the same protocol, carrier frequency and almost the same commands, so it is reasonable to assume the P3600 does as well. It is unlikely (but not impossible) that a manufacturer would change the remote and receiver in a earlier product to something different and then change it back again.
Generally speaking unless a later product has many different commands than an earlier version then they tend to use the same protocol etc as the earlier version