Yes, you are right - you did indeed read in a book that Kerry Glass used a 'reversed flame' pontil mark --- it was in my book!!!
As David points out, this was most probably as the original stamp was lost or damaged. However, please not that not ALL Kerry Glass is marked this way, and it would be right to suppose that any marked with a reverse pontil mark is most likely to be later than those that have the mark the right way around.
I interviewed the owner of the current Kerry Glass for my book - he was a blower and maker at the original Kerry Glass. Alas he was not able to shed any light on exactly what happened or when.....just to save anyone the time of contacting him and asking!!
Also, I'm not aware of any website or other information source about Kerry Glass other than items sold by Artius Glass, or similar queries on the message board at Isle of Wight Studio Glass. I was able to track down an original shape list, which appears reproduced in my book, along with a 2 page spread about Kerry showing the main colourways produced.