Yes, modemac is my main BSR info source and I basically just parrot what he says instead of providing original research. And that requires me to trust the accuracy of his research. So if anyone knows of inaccurate info on his pages, I would like to know so I'm not passing along bad info, or at least know better myself.
You're right, he makes no mention of these kettles (as well as some other BSR products)on any of the pages I've seen. For the tab lids, his best info is on the page for outdoor cookware. He says:
(more relevant passages bolded for better clarity)
"In 1967, the introduction of DISA automated production brought one major change to the design of the camp oven lid.
As with their saucepans, all Birmingham Stove & Range camp lids made during and after the year 1967 have tab handles rather than typical handles. These tab handles make the pot harder to lift, and persons using these lids would often use a hook or even pliers to lift the lid.
The tab handle was a cost-cutting measure used with lines of product produced in lower numbers. A lid with a handle required an additional step in the manufacturing process to produce the handle, while the tab lid could be molded at the same time as the lid itself. Far more dutch oven lids were produced at BS&R than camp oven lids; therefore, the additional effort and expense was made so that all of the dutch oven lids were made with handles. Fewer camp oven lids were made and sold, so these lids were made with tab handles to reduce production costs.
Dwayne Henson wrote on Facebook, 'Before the Mair lifter, most people used camping pliers, fencing pliers, channel locks, etc. to lift the lid. The problem with these was that often, people would often grip the coal retaining ring with the pliers and a bust out a section of that ring. That is why so many older CO Lids have 'bites' missing out of the coal retaining ring. Don't do this! Lifting that thick tab with pliers ought to work, but don't do that! Get a proper lifter. I have also seen where people run a loop of wire through the hole and use that.
But the tab was a very easy pattern for the mold to release with the DISA machines. CO [camp oven] lids were a smaller volume item and the lifting tab was a quick, easy, cheap way to get the job done. The higher volume items DO/Skillet lids had that opening finger handle redesigned to work with the DISA's.' – April 29, 2015"
http://www.modemac.com/cgi-bin/wiki.pl/Outdoor_Cookware_by_Birmingham_Stove_and_Range
So, though he only mentions camp lids and saucepan lids specifically, it implies that the tab lid handle design was introduced with DISA automation, not before. But if this is not true, I'd like to know.
I do agree the kettle design "looks" older...