  Dihadron azimuth correlations can provide combinatoric access to jet
structure in nuclear collisions. To isolate true jet yields a background must
be subtracted, including a constant offset and a contribution from "elliptic
flow" (azimuth quadrupole measured by $v^2_2$). The principle of "zero yield at
minimum" (ZYAM) has been introduced to determine the constant offset.
Independent measurements determine $v_2^2$. This analysis demonstrates that the
ZYAM concept is invalid (offset typically overestimated) and $v_2^2$ is also
overestimated by conventional measurements. Jet yields are thus substantially
underestimated in more-central A-A collisions, and the "away-side" azimuth peak
(back-to-back jet correlations) is strongly distorted, leading to incorrect
inference of "Mach shocks."
