[LargeFormat] Roman numerals on Zeiss barrel lenses

[Les Newcomer]

http://home.twmi.rr.com/lnphoto/zeissbarrel.jpg

The above link shows two  Zeiss lenses,  the top is a 25cm Tessar with 
the Roman numeral "X" and in subscript "2"

The lower lens is a Protar VIIa  with the roman numeral "IV" and in 
subscript  "1"

The owner of the Tessar also owns  two other lenses all marked "Ic"  so 
I assume they are Tessars.

He has an 18cm  marked  BVI  (sub 2)   and  a 21 Marked  VII (no sub)

Any ideas what these alien markings mean?

the only pattern I see is that the roman numerals increase in size as 
the barrel dia increases.

My Protar, at f7.7 is the smalles and is marked #4
The 18cm  f4.5 is marked #6  with an odd B in there
The 21 cm  also 4.5 has to be larger than the 180 and is marked VII
and the 25cm is marked "10"

Not sure if there really were three different sizes of barrels between 
a 210 and a 250mm, but it's a theory.