There are several different theories and different people do and try different things. The temps you are quoting are air temps, snakes can and will go underground where temps will be more evenly tempered. The Barkers have their own way of doing things and they use much cooler temps than most and feed alot less. I am in no way knocking them but if you read what other breeders do you will find many variations. I cooled one year and then didnt the next year and got similar results. I have some girls lay in Feb and other that just laid in Oct and expecting another to lay in November. The later girls obviously cycled and became gravid during the summer so cool temps didnt trigger them?Who knows
One thing Tracy Barker said that I follow is watch your females for breeding/cycling signs and if happens to be in July or Jan. pair them up. I have found that was the best advice I have ever got and now I breed according to my females behavior and history more than a specific time of the year. I know other breeders here in southern cali that cooled this year and some that didnt and I am hearing about alot of people experiencing late clutches. So who the hell knows? I think low pressure systems play into it alot as well.
I reccomend following what other successful breeders do and making adjustments as your experience increases and see what works best for you. I followed alot of the Sutherlands practices because they were(not any more) in my general area and figured their climate/temp changes were similar to mine. After a few breeding seasons under your belt you will get a feel for your girls and make adjustments that work for you.
There isnt necessarily one way to do it.