In PS 3.6 - 2008, page 7 one can find:

5 Conventions
....
Where an x is shown in a group or element number, it means all
values from 0 through F inclusive
....

shouldn't there be a note for group and "x" being an odd value ? I am
thinking that for Curve Data / Overlay Data, "x" can only even number
(ie [02468ACE]).

It becomes even more confusing when dealing with (7f01,0010) which
could be Variable Pixel Data or Private Group Length attribute at the
same time...

thank you