  Two contradictory results on the evolution of SO galaxies now exist in the
recent literature; either S0s are old ($z_{formation}>2$) and are evoloving
passively or most of them formed at $z<0.5$, as implied by the deficit of S0s
in intermediate redshift ($z\sim0.5$) clusters. The resolution of this
controversy may be that the apparent deficit of S0s has been derived from a
quantity -- the E to S0 ratio -- which is prone to morphological classification
errors. Once all sources of error are taken into account, the E to S0 ratios of
clusters at different redshifts are fully compatible, and no additional
creation of S0s at $z<0.5$ is required by the data. Furthermore, there is no
deficit at all of S0s in the intermediate redshift cluster for which we have
morphological types of very high quality, and thus derive an E to S0 ratio with
a small error.
