rad cowl heights

[JonE]

Been sitting in the archive cards trying to get my head around cowl changes.
One of the interesting things is different part numbers for "Austin" and "BO".. which latter I'm now presuming is 'built overseas'.

Could someone give me their best thought on the number of different cowl heights from '22-'34 i.e. forget about the different in surface finish or badge position. I'd thought there were only 3 (but that the shape of some inspired different thought perhaps), but now I'm not so sure...

[JonE]

       
some notes from Bryan Walker on the Original Detail group made in response to the index cards above...

"The change to Nickel plate / higher radiators started prior to the induction of the coil ignition, I suspect the A-16 and A8-4 is around the crank handle setup being different between the two types of motors both would have been the 1”5/16.
So far have the following changes:
1922 - Aug 1928 Low/ painted
Aug 1928 - sept 1928 High - 1”5/16 filler for mag mag 
Sept 1928 - sept1929? High - 1”5/16 filler for coil motors.
May 1929 - July 1930 high - 2” filler
July 1930 changes done for the short Scuttle cars to accommodate the longer bonnet and change to number plate fixing bracket (2 types of cowl listed BD199 & BD194)

Should have said for May 1929 2” filler type was until the long scuffle type ended"

Anyone else able to give precisely what the difference between the mag and coil part numbers is?
Or indeed, to account for the first mid sized 28-30 cowls which seemingly had the same curved base as per the earlier small cowl - rather than the flat?
Any more thoughts on the B.O. designation?