If you have a copy of the source that you've vetted, and you can compile it in such a way that the resulting binary is a bit-for-bit match of the developer released binary, then you know that either there is no future-activation code or you missed it in your review or your compiler was itself compiled maliciously with the intent of inserting malicious code into that exact version of truecrypt every time it was compiled. Or there is no future activation code.