  We analyze the robustness of H--deficient post--AGB tracks regarding previous
evolution of their progenitor stars and the constitutive physics of the
remnants. Our motivation is a recent suggestion of Werner & Herwig (2006) that
previous evolution should be important in shaping the final post--AGB track and
the persisting discrepancy between asteroseismological and spectroscopical mass
determinations. This work is thus complementary to our previous work (Miller
Bertolami & Althaus 2006) and intends to shed some light on the uncertainty
behind the evolutionary tracks presented there. We compute full evolutionary
models for PG1159 stars taking into account different extramixing
(overshooting) efficiencies and lifetimes on the TP-AGB during the progenitor
evolution. We also assess the effect of possible differences in the opacities
and equation of state by artificially changing them before the PG1159 stage.
Also comparisons are made with the few H-deficient post--AGB tracks available
in the literature. Contrary to our expectations, we found that previous
evolution is not a main factor in shaping H--deficient post--AGB tracks.
Interestingly enough, we find that only an increase of $\sim50%$ in the
intershell opacities at high effective temperatures may affect the tracks as to
reconcile spectroscopic and asteroseismologic mass determinations. This forces
us to conclude that our previous tracks (Miller Bertolami & Althaus 2006) are
robust enough as to be used for spectroscopic mass determinations, unless
opacities in the intershell region are substantially different. Our results,
then, call for an analysis of possible systematics in the usually adopted
asteroseismological mass determination methods.
