My memory says that 72deg was for roadsters, 73deg for "sporty" bikes, and 74deg for racing machines.
Maybe things have changed in the last 40odd years?
Looking at the 1986 Mercian catalogue of which I showed an excerpt, the King of Mercia Racing is 74deg, but the KOM Touring is 73deg. The 753 Special is 74deg and also the Professional and Strada Speciale too.
In fact, looking through the catalogue there's nothing at 72deg parallel, though one or two have 72deg head tube in the smaller sizes though they still have 73deg or 74deg in the seat tube.
Full carbon forks with mudguard eyelets
Re: Full carbon forks with mudguard eyelets
Mick F. Cornwall