The SML Gold Medal
#15xxx - #202xx1
Around s/n 15xxx, SML introduced the Gold Medal models (note that there were some crossover Rev. D altos and tenors available until 156xx or so). They are the pinnacle of SML design: rolled tone holes, elaborate engraving, etc. As a matter of fact, the name comes from the fact that these horns won a couple of gold medals at the International Music Festival at The Hague (Holland) back in the 50's for their excellent design and performance.
The horn is NOT just a repackaged "Rev. D", although they do look similar. The bow and neck of the alto and tenor are NOT interchangeable with their Rev. D counterparts, leading one to assume that the bore is completely different.
Based on the start date of these horns (around 1954-7), one can assume that they were introduced to compete directly with the Selmer Mark VI or the earlier Super Balanced Action.
These horns were the first and only models to feature all of the "22 Features" -- and, even then, only a few did (up to s/n 19xxx). At s/n 18xxx, the adjustble bell key felts (Feature #20) only appeared occasionally and 19xxx featured the end of the bell-lip engraving (Feature #16). At s/n 205xx, rolled tone holes were discontinued (Feature #19) and the King Marigaux stencil was introduced, ushering in what I call the "Mark II" version of these horns.
What this essentially means is that the SML's with the most features - sans the standard altissimo F#, which seems only to have been on late King Marigaux stencils - are found in the serial # range of 156xx to 18xxx. These horns should be the most sought after. I also think that the "Two Tone" finish of lacquer body and nickle-silver keys is fairly strikng and SML did consider this to be a "premium finish" choice. (There are still a fair number of people that think that this set-up is indicative of a student horn -- it isn't in the case of the SML!)
Oddly, I've never seen a Gold Medal in gold plate. I tend to think that this plating choice was discontinued or was only available as an "extra expensive" custom option.
Finally, the beautiful soprano contributed by Bill Kasper does not have "Gold Medal" engraved on it, nor does the baritone from Morgan Witthoft. (See the footnote on serial number oddities, below.1)
#202xx - #265xx
At approximately s/n 202xx, the Standard models disappeared leaving us with only the Gold Medal horns and some glorious stencils, like the King Marigaux. These horns were different from the first batch in one significant way: they were ONLY available with straight tone holes, as far as my sources and I can tell. (Other additional features became optional or were eliminated: adjustable bell key felts, extensive engraving on the bell, etc.)
This model was available until SML stopped saxophone production in 1981 or so -- around serial number 26xxx or 27xxx (although there may have been additional King Marigaux horns may have been produced, or at least "were available" after s/n 265xx).
My opinion: s/n 205xx was produced around 1967 or so. This is near the end of the manufacturing run of the most popular Selmer Mark VI's and Selmer had fairly well cornered the market on pro horns. I think SML was financially hurting and discontinued all other models to be a little more profitable and cost effective -- and if it's true that SML only used only straight tone holes at this time, that would support my theory (rolled tone holes are harder to fabricate -- and thus, more expensive).
Note that at about 26xxx the engraving changed on these horns and no longer featured "Gold Medal" (SML may have also changed their marketing to reflect this). I have also heard reports that horns after 25xxx may have non-functional adjustment screws for the upper and lower stacks: even though they're present, they don't work. Possibly more cost-saving on SML's part.
For further information, please see the SML Comparision chart.