Maximum dB SPL from a digital microphone
Mostly yes. See http://www.analog.com/en/analog-dialogue/articles/understanding-microphone-sensitivity.html

You need to be aware of the difference between peak and RMS level. The max SPL for a sine wave would indeed by 120 dB SPL. However the max SPL for something like a trumpet would be significantly lower, at least if you define SPL as "what I would see on an SPL meter.

The difference is the crest factor of the wave form: for a sine wave with an RMS of 120 dB, the peak level is 123 dB. For a trumpet with 120 dB RMS, the peak level will be around 140 dB or so. So the microphone will clip way earlier on a trumpet as compared to a sine wave.