How can I see the correct dBSPL of a saved spectrum in SysTune?

Unfortunately the measurement calibration is not saved in the spectrum file by SysTune.
If you need the calibrated Spectrum of the saved "Time Signal" then you need the pressure calibration for that measurement.
(the number of RMS Pressure [dBSPL] for zero RMS Level [dBFS] in the "Use Pressure" calibration window)
The best is that you write it in the name of the file itself. (for inst. "Spectrum 117.3dBSPL.etm")
If you load this file later and you show the Spectrum you can see the data in dBFS (-48.1 dBFS for 1kHz for instance) first.
To see the 69.2 (dBSPL) you have to add the calibration of (117.3) This is done easily by adding a gain in the Virtual EQ plug-in.
If you do not have that calibration number, please repeat the calibration and find it in the calibration window then.
You will see the correct dBSPL numbers then in the Spectrum, although the unit shown is dBFS.