  Usually, in order to compute an anomaly (be it chiral or trace) with a
perturbative method, the lowest significant order is sufficient. With the help
of gauge or diffeomorphism invariance it uniquely identifies the anomaly. This
note is a short review of the ambiguities that arise in the calculation of
trace anomalies, and is meant, in particular, to signal cases in which the
lowest perturbative order is not enough to unambiguously identify a trace
anomaly. This may shed light on some recent contradictory results.
