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Not an expert - but in doing research on my 1016, I think the Swiss T <25 on at 6 o'clock came in 1963 onwards so may not be a 1961 version unless it is a replacement dial. I have a 1962 with original certification and a serial number beginning 745. If the serial number of yours is higher than that then it is definitely later than 1961 and vice versa of course.
The "T" was apparently added to indicate Tritium being used in the lume and was sufficiently low in radiation to meet US max requirements for radioactivity - the "<25". My dial has the exclamation point ( a dot below the 6) which according to the articles I have found was an interim way of identifying non radioactive lumed dials.
I do like the domed crystal which mine does not have, the original having been replaced by a service crystal many years ago. The domed crystal does add to the overall design and adds to the appeal of the already appealing dial
1961 explorer anybody? Model ref 1016 . Sadly no box or papers.
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