Well idk about p99 but according to EQEmu source (which p99 came from) there is no higher chance to proc the first time you swing a weapon.
Take a look at TryWeaponProc, ExecWeaponProc, GetProcChances in zone/attack.cpp there is nothing keeping track of whether or not its a weapons first swing.
link
https://github.com/EQEmu/Server/blob...one/attack.cpp