You could test it yourself..
One will be set before the other, so if you put something like
on X pressed
spawn projectile at layer 1 point 0
if var2=0 then projectile set instance var1 to 1
on projectile created
if var1=0 then projectile set instance var2 to 1
So whichever event gets run will show you which is set first. You'd use the debugger to check the values.