Thank you once again for this additional and very useful info.
As it relates to the Harrisburg precancels previously discussed, here are a few more that I found which:
(1) Documents R.CO. use in Jul '39 and Jan '40;
(2) Documents GBC use in Sep '41 (and on a 2-cent pair); and
(3) Documents another WFH-1 (Oct '41) although a bit more smeared than than the previous example I posted.

I guess I'll have to keep looking for more of these varieties.