This article examines the differences in the 1st, 2nd and 3rd Series / Generation of the Taurus Millennium and Millennium Pro pistols. It gives some insight into how Taurus designs have evolved over time.
While I do love my PT-111 Pro (that’s 2nd series, stainless, full “Millennium Pro” scroll!), it does appear to me as if Taurus might be utilizing its unique position in the market to continually test and improve their design, effectively using their customers to beta-test and otherwise improve their product line. At least, I hope so: otherwise it’s just neurotic!
An interesting read even if you do not have a Taurus Millennium pistol.