How can millisecond pulsars transfer the accuracy of atomic time?

Atomic time scales like TAI and TT(BIPM) get their accuracy from primary frequency standards (presently Caesium fountains) which realize the SI second. The rotation period of some millisecond pulsars is so regular that they may provide information on the long term stability of atomic time scales. As atomic frequency standards continuously improve, atomic time progressively outperforms the rotation of pulsars. Nevertheless millisecond pulsars could be used as a flywheel to transfer the accuracy of newly developed standards to the past. We study the factors that may limit this transfer and estimate the accuracy that could be reached, with examples based on real pulsar data.