Until, well, 15 minutes ago, I'd assumed Barclay Perkins Old Burton Ale, KKK was a winter seasonal. Then I saw this:
DRAUGHT BEER ORDERS - EASTER 1944.
In order to ensure delivery of the above, will you kindly order at least two thirds of your requirements for the 2 weeks including Easter, of KKKK., KK., and XLK, so that they may be delivered during the week March 27th to April 1st.
The Ales (A., X., and X.X.,) required for Easter should be ordered for delivery during the week April 3rd to 7th.
Barclay Perkins Circular Letters held at the London Metropolitan Archives, document number ACC/2305/01/521/1.
That explains why I've found brews of KKKK in January and February as well as September and October, as you would expect.
I've seen other references to the Easter trade, which imply that it was one of the peak periods of demand for beer, along with Christmas and New Year.
Note that the Burton Ales and Bitter needed to be ordered a week earlier earlier than the Mild Ales.Which implies that the production of these beers took longer.
Still learning so much from looking just a little bit closer at the material I already have. And in some cases have had for ages.