Tim H in the comments to the last post had asked about the dry-hopping of stout and porter, pointing to some evidence it was done. Dry-hopping means adding a handful or more “dry” (unboiled) hops to the beer when barrelled or sometimes when stored in a vat or tank before barreling.
At p. 400, here, from A Textbook of the Science Of Brewing (1891) by Edward Moritz and George Morris, you will read that dry-hopping was generally not used for stout and mild ale.
The reasons are evident from the way Moritz explained the advantages of dry hopping. It was primarily for bouquet and taste in pale ale, and also to stimulate an after-fermentation for long-stored beers. Export stouts were the latter case, so that Brettanomyces yeast would consume the non-fermentable (by normal brewers yeast) dextrins and complex sugars.
In contrast, for mild ale a fresh, sweet quality is sought, where the malt comes to the fore. The hops play a moderated role vs. pale ale. Porter was increasingly sold fresh in the 1800s and there too malt is the signature, except roasted malt. I think likely a flowery or herbal note was felt to clash with fresh porter or stout and the hop quality wanted (in general) was a neutral bitterness only.
Certainly porters as handed down to us before the craft era, in my experience, did not have strong hop smell and taste: Sinebrychoff Porter, Carnegie Stout, Anchor Porter, Molson Porter, the surviving U.S. regional porters, Guinness, Murphy, Beamish, Sheaf Stout, Lion Stout, the East European porters: none of them had a pungent hop smell that one would associate with dry-hopping.
Many of these survive and remain unchanged in this respect.
To me, this confirms what Moritz and Morris stated. Moritz was a highly regarded brewing scientist of the Victorian period, it might be added.
To my best recollection Frank Faulkner stated the same thing or one can infer it from his directions on how to brew stout. I recall as well similar statements in issues of the Journal of the Institute of Brewing. Wahl & Henius in the U.S. too.
Did some breweries diverge from what might be viewed as a rule of thumb? Yes, Moritz himself noted this. But this was not typical, judging by the way an experienced scientist presented the matter.
20th century practice is less significant IMO as gravities had fallen and dry-hopping can encourage stability, as Moritz noted too. Nonetheless the pre-craft porters and stouts I can think of hewed to Moritz’ statement. It was only with the onset of craft that one started to see aroma-hopped porter and stout.