There is a field called 'level2' in the player profile struct:
common/eq_packet_structs.h
Code:
/*0241*/ uint8 level2; //no idea why this is here, but thats how it is on live
level2 isn't referenced anywhere in the EQEmu code, so presumably it is set to 0 at character creation and never changes. You could try storing the max level reached in here, as that is possibly what it was intended for. I just looked at three of 6.2 era packet collects and the level2 field was always the same as the level field in those collects.