  The concrete evidence adduced to support the widely held idea that
unidentified infrared bands (UIBs) are enhanced in carbon-rich planetary
nebulae (PNe) is a remarkable UIB 7.7 {\mu}m versus C/O ratio correlation plot
for six PNe, obtained from air-born observations and published in 1986 by M.
Cohen and coworkers. However, the space-born data presented by Cohen & Barlow
in 2005 undercut this correlation, and I show that the larger dataset they
provide disproves a specific link between UIBs and carbon abundance in PNe. It
also follows from these data that interstellar UIB carriers cannot originate
from the atmosphere of carbon-rich PNe.
