Unfortunately, my copy of Opie is packed away and inaccessible for at least a month.
I have checked mine*, and I find the entry on Baa, Baa, Black Sheep rather puzzling. After giving the standard current form. all the Opies had to say about this rhyme was:
The words of this favourite rhyme have scarcely altered in 200 years:
Bah, Bah, a black Sheep,
Have you any Wool,
Yes merry have I,
Three Bags full.
One for my Master.
One for my Dame,
One for my Little Boy
That lives in the lane.
In the wool trade the division of the bags is said to refer to the export tax on wool imposed in 1275, The words are sung to the old French tune ‘Ah vous dirai-je’.
A list of historical printings and mentions follows, as is standard for the book; and that’s it. No further comment at all. And yet the Opies certainly knew that what people in the wool trade like to assert about the origin of a nursery rhyme is no evidence at all; but that many if not most of their readers would not, so that mentioning this belief without explicitly pointing this out would mislead people into thinking they were giving credence to it. And in fact it blatantly has: the Wiki entry which states that “This has particularly been taken to refer to the medieval English “Great” or “Old Custom” wool tax of 1275, which survived until the fifteenth century” gives Opie as a source, which implies quite falsely that the Opies themselves took it so. But it beggars belief that the Opies could have wished to give the impression that a rhyme first sighted in the mid-18th century had anything to do with a customs duty imposed in 1275!
FWIW, in The Real Personages of Mother Goose (which the Opies described as ‘a curious mixture of fact and fable, and a cheerful determination to prove that the nursery characters were real persons regardless of what the sources quoted say’) Katherine Elwes Thomas asserted that the rhyme originated in poverty and unrest in the reign of Edward IV, when wool was so profitable that vast areas of land were given over to sheeepwalks and “there was scant call for field labor’, and that ‘“My master” and “my dame” symbolized the kind and the over-rich nobility, with the “little boy that cried in the lane”, the common people, who, thus coming out the small end of the horn in the scant thirds allotted to them, only too frequently had their cries stifled by the hangman’s noose’. She cited no evidence whatsoever for this, any more than she offered any evidence for Cardinal Wolsey being the original Little Boy Blue, Mary Queen of Scots being Little Bo-Peep, or Richard III being Humpty Dumpty.
*I have the 1952 edition, but by searching the ‘look inside’ feature for the 1997 revised edition on amazon.com, I find that the only change to the Baa, Baa, Black Sheep entry was to alter ‘in 200 years’ to ‘in 250 years’.