Yes. That's my post - I've been searching a long time! Helen Duff stated her father was Alexander Duff "labourer (deceased)" when she married 27 Feb 1869, and that was the only evidence I then had about her father's occupation - and even then it's only her say-so that he was a labourer (or, indeed, deceased).
I later found that Banff Kirk Session of 22 Jun 1835 records that Helen Duff's mother, Janet Cruickshank, accused "Alexander Duff cooper at present in Huntly" of being the father, which he had admitted in a letter to the Kirk Session, promising "to satisfy everything that was required both as respected to the church, and the future maintenance of the child".
Even later, I discovered the Huntly Kirk Session, on 11 Dec 1837, found "Alexander Duff, Cooper, Muir of Rhynie, guilty of antenuptial fornication.". This Alexander Duff can only be the Alexander Duff Cooper who married Isobel Gordon in Huntly 25 Dec 1834, whose first child, also named Alexander, was born in Huntly and bapt 23 Jan 1836, whose second child John was born in Moor of Rhynie on 9 Dec 1837, and who all appear in the 1841 census in Muir of Rhynie the father being "Alexander Duff Cooper", age recorded as 35 (and not born in Aberdeenshire) against wife's recorded age of 25 (actually 27).
Even later still, I found Isobella Gordon [sic] in 1851, now widowed and with family, in 1851 in Old Machar; she died 3 Apr 1888 in Woodside, Aberdeen, husband recorded as Alexander Duff Cooper (Master).
There is no record of Helen Duff's birth in Banff - I can infer Apr-Jun 1835 from censuses which fits well with the KS. It would seem that Alexander Duff left Janet Cruickshank to her own devices and married Isobel Gordon, perhaps not realising Janet was with his child. Whatever the precise circumstances, one cannot argue anything other than that Isobel Gordon's husband is the father of Helen Duff.
So, the identity of this Alexander Duff? The 1841 census implies he was born 1801-1806, in all likelihood in Banffshire, but this cannot be taken as gospel, only a guide. One suggestion recorded in the only Ancestry tree for Alexander Duff & Isobel Gordon is that Isobel Gordon's husband is son of Auchindachy's James Duff & Helen Smith. He was born 9 Oct 1807, and thus should have been recorded as 30 in 1841. Even so, given Helen Duff's story-telling, it's a suggestion worth pursuing. If someone knows what happened to Auchindachy's Alexander Duff then of course this suggestion can be discounted. Hence my query.
I hope that clarifies the situation. Now, if anyone can suggest other parents for this Alexander Duff.....