So I must conclude that the numbers I've got that are not in your
list, are
from the suburban offices.

Blair's list includes all the surburban offices. At a quick glance, and
as one who lives in one of the outermost London suburban postal areas,
I think it goes to the present day.

For example, I've got more than 4 numbers for East Central London.
According
to my stock, it goes to at least 78.

According to http://homepages.gold.ac.uk/genuki/L...ldistricts.htm
the number suffixes did not come in until 1917, so they must mean
something else on your Victorian postmarks, but I can't tell you what.
A Google on "london postmarks" comes up with a number of sites, some
with book recommendations, including "The Postal Cancellations of
London 1840-1890 by HC Westley" which sounds like what you need, but
I've never seen a copy.

Chris