I'm assuming you are always solving with ICRS.
When you select "automatic limit magnitude" it searches through the GAIA files (in magnitude order) until it finds a magnitude that give a "sensible" star count.
For each DR3 file it searches, it outputs a pair of lines like:
Gaia: Global context
x.xx us
(after the first pair of lines it outputs "Searching for optimal magnitude limit..." - but just ignore that)
If you have changed the GAIA preferences to only include the first four DR files ( files -01 to -04), then it should not be able to output more than 4 of the pairs of lines.
when it has finished searching, it outputs something like:
* Using an automatically calculated limit magnitude of yy.yy.
The question I was trying to answer is, with "automatic limit magnitude" checked, how many of these pairs of lines (i.e. how many times does it say "Gaia: Global context") before displaying the calculated limit magnitude, and what is this magnitude?