Well done Tony.
Frank, your findings are extremely interesting and not at all paradoxical.
The use of such a proportion of wheat flour is the principal difference between prepared mustard from the North Buckinghamshire area around Newport Pagnell and Olney and that made in the Norwich region. These were the two principal mustard growing regions in England during the first half of the 19th century, and the two dominant brands were and still are Taylor's of Newport Pagnell and Colman's of Norwich.
Taylor's mustard is now made in Cheshire. Some years ago health and safety inspectors condemned Taylor's little factory in Newport Pagnell as not up to regulations. Steven Taylor spent a considerable sum obtaining plans for upgrading the premises, but on submitting these to the planning authority, found that they were refused because the building was listed as of historic interest!
Mr Taylor told me that he was going to abandon mustard production completely and retire, but eventually teamed up with a specialist manufacturer in Cheshire. Their main difficulty was the local water, which imparted a rather different flavour to the mustard. That problem has now been resolved.
I know that Steven Taylor attempted to find a way of eliminating wheat flour from the recipe, at the request of local coeliacs intolerant to wheat flour, but it proved impossible without changing the whole character of the mustard.
So, it seems as if the wheat flour in the North Bucks Double Superfine recipe provides rather more in characterics than just a bulking agent. My partner, Janet, explained to me that the starch in wheat flour thickens by creating a stronger lattice through which water can still flow but at a reduced rate, rather than by a gelatinisation process typical of many other thickening agents. You can also appreciate Mr Taylor's probable unwillingness to get involved in unnatural additives.
On a different point, most commercial mustard pots were ceramic rather than glass. However one of the rarest is a late Victorian amber glass pot made for Taylor's with relief lettering. I have never even seen one - just the photograph in Blakeman & Smith. Please would readers let me know if they come across one.