A suggestion:
Back in MK9 era we used mostly "~" notation, denoting that it meant buffering during startup of previous move because, obviously, this is how it worked in the game.
"xx" was mostly used in other games (I think SF community uses that for the most part?), and traditionally cancelling in most games was done differently than in NRS games, by inputting required stuff during previous move's recovery.
Since MKX we've actually seen both methods in place: pre-buffering was still the to-go method, but some moves (Mileena's teleport into air sai, for example) worked differently, like it does in many non-NRS games.
Perhaps, similarly to how we adopted and formalized the difference between 2 ways of using meter versions of moves (pre-burning and post-burning), we could do the same with cancelling, just in case there will be moves with different cancelling windows in MK11?