I purchased four Nest Protects from Best Buy. Two were manufactured in
2022 and have the UL 217 rating label. They also have a Smoke
Sensitivity number stamped on the label of .96+/-.50%The other two were
manufactured in 2021. They don't have the UL ...
I never did get an answer, and the article doesn't say whether there is
any functional difference between the two models I described, both of
which are 06C but have differences as I listed in the question.