A pilot's report of leaving an altitude on a PD descent/climb cannot
be used to assign the altitude reported leaving, but it can be used to
assign an altitude that provides minimum vertical separation from that
altitude, so it is still useful.

Hmmm...is there some section that expressly allows that, or is it
allowed because not expressly forbidden? ;-)

I would have interpreted the following section to apply to that
scenario as well, since the implication is not to permit verbal
reports to be sufficient for separation purposes, period, in PD
descents.

-------------snip-------------------
b. Assign an altitude to an aircraft only after the aircraft
previously at that altitude is observed at or passing through another
altitude separated from the first by the appropriate minima when:
....
3. The aircraft previously at that altitude has been issued a
climb/descent at pilot's discretion.
-------------snip-------------------

Can you shed light on the logic?

Where is that written?

-------------snip-------------------
Non-Radar
6-6-2 Exceptions
Assign an altitude to an aircraft only after the aircraft previously
at that altitude has reported at or passing through another altitude
separated from the first by the appropriate minimum when:
....
c. The aircraft previously at the altitude has been:
1. Issued a clearance permitting climb/descent at pilot's
discretion.

-------------snip-------------------