Hello mautschi, I'm not sure how it works, but the command to load a saved core is in the campaign.pzdat file. If you compare the GC39 campaign.pzdat file with the GC40 campaign file, you will see that the GC40 has two extra commands in the section 'Entry points'. The 'END_SAVE_CORE' command is added to the 'Entry points' in GC40, with a long code put in front of it. So my guess is this is used to load an earlier core.
So I think the GC40 loads the previous core through the 'Entry points' line, with the same command END_SAVE_CORE, and the code displayed in the previous column (it begins with {C6FE45B9- in the case of GC40 )
This probably is the file header code that it searches for in the saved core, so it knows which ones to choose. In the 'SaveCore' folder on my computer, I can not open the core files properly, they seem to be coded, but from what I can see the file header code is the same as the numbers in the campaign.pzdat point to.