I agree that there are many limitations to CBC counts. But for some species
and locations they are the best information we have.
I believe it is possible to extract useful information sometimes (see the
article
"Effects of ENSO(El Nino) and PDO(Pacific Decadal Oscillation) Events on
Seabird Populations as Revealed by CBC Data" in the latest issue of
Waterbirds (Vol 23, no 3, p. 416)

I have been frustrated by the unwillingness of Birdsource(Cornell) to include
party-hours in its database. Two years ago they seemed receptive to the
suggestion.
Bob Vandenbosch