My _guess_ is that that probably happened because there is no formal
'model'
for that first one (unlike the first -11, which got re-named the -11/20
BITD), and people recently picked that to disambiguate them from all the
other -8's.
The original PDP 11 was sold in two model options, although the numbers did
not appear on the faceplace, very clearly the model options were called PDP
11/10 and PDP 11/20. These are just as legitimate and well defined as the
11/05 vs. 11/10 (later version) that followed it except for the one fact of
the front plate. The fact that the name does not appear on the front panel
has caused every DEC historian to miss this factoid. Read the first
brochure, don't take my word for it.
http://vintagecomputer.net/browse_thread.cfm?id=593
Momentum prevents change I get it, but it's clear that the model 11/20 and
11/10 existed from day one. The problem is that DEC re-used the 11/10
model name again a few years later, the other cause for neglecting the
original 11/10 model.
Bill