Summary of the situation (as it seems to me).

DP is currently taking too long to produce texts that are are either less (plain-text)
or more (DP-style HTML) than the supply chain is able to convey to the end-readers
to deliver the experience intended.

Once DP delivers their content in one or both of those formats, it's for all purposes
stuck at PG (nicely symmetrical with how it had previously been stuck at DP) because
while DP had the raw materials but no finished goods, PG has the finished goods
but no raw materials. So for whatever purpose (quality improvement, error correction,
evolving requirements) PG's products grow stale.

What can DP do in the reasonable short-term future that would be low risk and low
effort?

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.