"Peterson’s Dublin & London line, stamped “London & Dublin” when made in London, seems to have debuted around 1940. I base this on the fact that the English factory on White Lion Street opened in 1937 and K&P’s November, 1938 Punch ad makes no mention of it."
So, Dublin & London, and London & Dublin are two different things. we see from pipedia,
"1895 Kapp and Peterson moved to bigger premises at 111 Grafton Street Dublin and also opened a new depot in Broad Street London."
So from the link I posted,
"The Patent Era was between the years of K&P's formation until the expiration of the patent; 1875 through approximately 1910. Though for our purposes we will list this era as 1875 through 1922. Peterson pipes made during the majority of this period had no "Country of Manufacture" (COM) stamped on them. However, later in this period, say around 1915/16, Peterson began stamping their pipes "Made in Ireland" in a block format."
So It's interpeting multiple data points...