>The first most obvious to me is to start getting serious about passing along the
raw materials. Upload in as complete form as possible the matching image and
text files so future modification and adaptation is possible. There's no loss to
DP by doing  so; and the risk is that over time they are quite capable of losing
track of them.

I suggest that it is helpful if possible for the HTML to be submitted with the linebreaks the same as the original book, and that PG retain those linebreaks rather than changing the line lengths by say running the HTML through “tidy.”  Or else at least retain the submitted HTML internally with the original linebreaks to make it easier to fix problems or make another pass through DP or some other process some day.  Pgdiff can be used to recover the linebreaks, but it is less work if the linebreaks are never discarded in the first place.