The only IEEE 802.11 PLCP headers that use a single parity bit are the ones used with the OFDM PHY and the ERP PHY with OFDM data rates. All the other PLCP headers use CRC-16.
Since the OFDM PLCP parity bit is used in conjunction with other sanity checking of PLCP header values the opportunity for all the right bits to flip and not produce a PLCP format error gets even slimmer.
I think we can live with it.
I hope this helps. Thanks. /criss