That's right, the library listens for the incoming stream and checks if the same data shows up 3 times in a row to be sure it's real data.
The HT12D does that, too, according to documentation provided in data sheets.
When there is something wrong, the threefold checking is aborted and an error code is returned by the library.
I couldn't imagine someone would use the address bits as data. Anyway, the library can be customized for your need just by changing how you instantiate the library (that means you'll most probably need to work on HT12E::HT12E()).
Cheers,
nu