I have recently developed a "thing" for the S&W 39's. So far, I have acquired two almost NIB's 39-2's and thought you might enjoy what I have discovered. The earlier one was manufactured in 1973-74 and the other in 1981. Now for the differences. While the boxes look identical at first glance, the older box has SMITH & WESSON, 9MM AUTOMATIC PISTOL, (DOUBLE ACTION), BLUE FINISH - Model 39 embossed on one end of the box top in silver print. The later box does not have this, and instead has a printed label that reads, 0392014001, MOD 39 9MM AUTO 4IN BL glued to one end. (Also has a "Y" floating around by itself.) Both have the upside down glued regular label on the other end. The older box also has the Statement of Liability and Warranty printed on the inside of the lid and dated April 15, 1955. The newer box does not.
I also noted that the older pistol has PAT'S Pending stamped under the ejection port while the newer pistol is blank. The slide locking notch is also deeper on the older pistol than on the newer one.
Thought you might enjoy those observations.

Armyphotog: Check the width of the retaining springs for the rear sights; some are a lot narrower than others. At this late hour I don't remember which is earlier.

I hate to speak up and expose my ignorance, (and remove all doubt as the saying goes), but where might I find and eyeball a retaining spring for a rear sight? If I failed to mention it, perhaps I should, I'm no expert, still a learner.

Probably I'm the one who'se ignorant; it looks like the leaf spring on the 39 rear sight that retains it in the slide, is an integral part of the sight, not a separate spring. Tell me more about the spring you need.

There also can be some plum coloring in the slide and decocker. Here is one that I gobbled up a couple of weeks ago:



The slide is just barely plum, while the decocker is much more.

And my label is much different:

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