‘T Swiss T’ v. ‘T Swiss Made T’ Day-Date dials

[miamiclay]

Is there even an approximate date when Day-Date dials shifted from “T Swiss T” to start showing “T Swiss Made T” instead?

It seems that many of even the earliest 5-digit DDs, the early 18038s and similar, have “T Swiss Made T” dials. I’ve seen TSMT on 180xx with serial #s as early as 1978-9, but I’ve also seen TST on other 180xx examples as late as 1986, and I can’t discern any consistent pattern.

I assume TSMT was *not* the standard text for all 5-digit tritium DDs right from the outset, or they would never have printed any flat, non-pie-pan TST dials in the first place. (Unfortunately, there is not nearly so much scholarship or research on the intricacies and details of the DD models as there is for the tool models, and the transition dates for when dial changes occurred in the DDs vs. the tool models often don’t match up.)

Is there a year or serial number before which 180xx models showing “T Swiss Made T” are presumed to be service/replacement dials?