Sure enough, I've found something new. I'd thought Maclay had been the first to come up with the idea of adding oats to Stout. It looks like perhaps they weren't. This is the first mention I can find of Oatmeal Stout:
"THE ARGYLE AND SPIRIT STORE CO.,
ANLABY ROAD, HULL
THE A.W. and S.S. Co. being Importers and Large Purchasers, with cash advantages, are in position to offer their customers exceptional value.
SHERRY } 1/-, 1/3, 1/6, 1/9, 2/-, 2/6, 3/-, 3/6
CLARET } and upwards
BURGUNDY, 2/-, 2/6, 3/-, 3/6, and upwards
CHAMPAGNE, 2/8, 3/6, 4/3, 6/-. Do.
HOCK, 2/-, 2/6, 3/-, 3/6, Do
(Thoroughly Matured by Age).
WHISKEY (Irish or Scotch), 2/8, 3/-, 3/4, 3/6, 4/-
FRENCH BRANDY, 4/-, 4/6, 5/-, 6/-, 7/-.
RUM, 2/8, 3/-, 4/3.
NICHOLSON'S GIN, 2/-, 2/4.
ROSE'S FAMOUS OATMEAL STOUT.
Jacobs' Pilsener Lager Beer.
Bass's Ale in Cask and Bottle, at Brewery Price."
Hull Daily Mail - Monday 18 January 1892, page 4.
An Oatmeal Stout wouldn't have been possible just over a decade previously. Because as we know, unmalted grains weren't allowed before 1880. An Oat Malt Stout would have been possible, but I can find no evidence of anyone having brewed one.
This later advert tells us a little more about the product, confirming it was made with oatmeal rather than oat malt:
"OATMEAL STOUT (Rose’s) most nourishing and strengthening, strongly recommended for Invalids. See medical opinions. Brewed from Oatmeal, Malt, and Hops only, 2s 3d per dozen. The trade supplied in Cask or Bottle. J. Wallace A Co., 35 George Street.Who was Rose? This tells us a little more about them:
Aberdeen Journal - Saturday 27 January 1894, page 2."
"BREWER'S PATENT CASE.Now isn't that confusing? Rose and Wilson had earlier taken a patent for both Oatmalt and Oatmeal Stout, but only used oatmeal. Given that, I can't see why Mr. Fraser (presumably of Maclay) could have been granted any sort of patent. But that is exactly what happened. A patent they robustly (but ultimately vainly) tried to uphold.
LOCAL FIRM OPPOSES CASE.
The application of Mr A. Fraser, brewer, of Alloa, Lanarkshire, Scotland, for a patent for oatmalt or oatmeal stout, was opposed by Messrs Rose and Wilson, brewers, of Grimsby and Hull, on the ground of its having been previously patented by them, was heard at the Royal Patent Office Courts, London, on Wednesday, the 16th of October. Mr Douglas appeared for the applicant, and Mr Goodeve, patent barrister (instructed by John E. Walsh, patent agent, Halifax, Leeds, and Hull) for the opponents. The Comptroller-General gave his decision yesterday as follows:- That Messrs Fraser's claim for malted oats is anticipated by Messrs Rose and Wilson's prior patent, consequently that claim must be struck out; and the other claim for a combination of materials with malted oats, only allowed conditionally that a special reference is made to Messrs Rose and Wilson's patent, who are the first patentees and users of malted oats for brewing purposes."
Hull Daily Mail - Friday 01 November 1895, page 4.
I still feel that I don't have the full story. But I'm getting there.