Terry Pinnell wrote:
I gather the numbers are in groups, often based on the distance from some
base, or on the number of blocks. So I can just about see how that
accounts for such large numbers. But can anyone please explain why the
gaps between adjacent houses are not simply 2, instead of 4, 6, 8 or 10 -
not to mention 34? I can't detect any logical pattern at all!

I looked closer at your pic and I'm pretty sure that I have the answer.

When the street was built, but before there were any houses on it, it
was already established where the "hundred blocks" were to be.
20700 was at a certain point, 20800 was at a certain point, 20900 was at
a certain point, all equidistant from each other. When houses were
built in the 20900 block, for example, they started at 20900, and
increased the numbering by a small number, like 4, 6, or 8. By the time
they had arrived at 20966, they had reached the spot where 21000 was to
start. And this is what accounts for the gap of 34 between 20966 and
21000.

--
K.

Lang may your lum reek.