Respectfully, some FACTS for you.
"GP" Thinners are not all the same thing. They do not all come from the same plant.
A quick check of the contents on the label will confirm this. They may be very similar but most will be subtly different blends of solvents.
The good news for punters is, that for the purposes we use them for they are equivalent. It is highly unlikely that modellers would notice any change in switching from one to the other.
Andrew P (A1)