I note that the RAK3172-SIP low level radio files use TCXO_CTRL_3_0V and (1UL), but it is not safe to assume that the RAK3172-T uses these same values.
There was a link posted in a different thread supposedly to the datasheet for the TCXO but the link goes to a regular crystal instead.
I note that the datasheet gives the TCXO a working temperature of -30°C to +85°C. This doesn’t match up with the RAK3172-T claiming an operating temperature down to -40°C.
I understand the TCXO will probably still operate at -40°C and the limit will probably be that it just doesn’t guarantee the stated +/-2.5ppm accuracy.