This may be well known to you but FWIW, the "P" of P454 confirms its Parechoc shock-resist system. The difference between the 454 and Chronometre Royal variant (both based on the 453) was six additional parts, most noticeably a stop lever which acted directly on the balance wheel when the crown was pulled. This is why the caliber's full name is P1008/BS, "BS" for Balancier Stop.