The formula you need to use is on p.32 of the SX1231H data sheet:
BW20dB = 2 × (FDEV + BR/2)
That gives an approximation for the width of the occupied channel (without guard bands, allowance for main crystal precision/drift, transmit spurs etc) so is the tightest you could expect to pack channels together and expect success.
You then need to map this against the FCC bandplan for that ISM band. There are several zones with differing rules about maximum radiated power, duty cycle etc. so that is quite an exercise.
Of course, as a shared resource, you have no guarantee that any particular "channel" is unoccupied at any point in time or that other users are following the duty cycle requirements.