(Some info from Antiquorum - originally posted by fabio6006)
Ref. 3970 It was once possible for astute collectors to acquire the rare Ref. 3970s for a fraction of its retail price.
Since that time, however, several factors have contributed to a sudden and sharp (but not entirely surprising) rise
in value for this watch. The Ref. 3970 is now truly considered a classic by collectors, following in the footsteps of
its predecessors Ref. 1518, Ref. 2499, and Ref. 2499/100. They have become virtually unattainable to all but the
wealthiest and most patient individuals. Obviously, the next best choice will be a Ref. 5970. Hopefully, this note will
shed some light on the different variations of the Ref. 3970 and help to better define its value, while clearing up some
misconceptions. The Series: One can distinguish three series in the production of Ref. 3970. We define a “series” by the
variation in case designs or features, whereas we designate dial variations as being “first generation”, “second generation” ,and so on.
As a general rule, the Ref. 3970 was produced in 18K white, rose, yellow gold, and platinum, with platinum being
the rarest variation, therefore always the most expensive. The first series of Ref. 3970 featured the 36 mm. case
with a snap-on case back. This particular model should be considered extremely rare since it was only produced
in fewer than 100 examples from 1986. The second series of Ref. 3970 also featured the 36 mm. case, but with
a solid screwed back. After the second series, Patek Philippe introduced the Ref. 3971, similar in design to the 3970
but with a sapphire crystal display screwed back. The company also received many special order requests to make
the 3970 with an additional sapphire crystal display screwed back. The third series is known as Ref. 3970E
(E stands for étanche which means waterproof) and was housed in the same 36 mm. case.
Because of numerous special order requests, Patek Philippe took the opportunity to feature the 3970E with both
a solid gold screwed back and a sapphire crystal display screwed back. This is probably the most common of the three series.
The earliest examples of the first series of Ref. 3970/2 with 36 mm. case featured a gold bracelet fixed to the traditional case;
subsequently an integrated bracelet was used. A small number of early Ref. 3970/2 watches were sold with a solid snap back.
Such watches should be considered quite rare. The remainder of Ref. 3970/2 will be encountered with the more common screw back.
Finally, in the first and second series, the watches were generally sold with tang buckles, whereas in the third series
(Ref. 3970E), after 1997, a deployant buckle was added. The Dials : when Ref. 3970 was first introduced, Patek Philippe
would occasionally accommodate a special customer’s request to order a custom dial. This often took place after the sale
was concluded and resulted in some interesting and extremely rare case/dial combinations. As time went on, it became
increasingly rare that the company accommodated requests for special dials. Consequently, any interesting or unusual dial
variation can add tremendously to the value of the Ref. 3970 and Ref. 3971.
Let us now examine the two generations of standard dials: The first generation dial of these references was offered in
two-tone silver (very subtle) with bâton markers. Generally speaking, the printing will be lighter on earlier dials,
and the numbers on the date wheel will feature a serif font. The dials may be variously described as satiné silver or opaline silver.
The second generation dial is silver (not two-tone as in the first generation) and features the same bâton markers,
but the font used on the dial will be slightly different, and the date wheel will be without serif.
The third generation dial is silver, but with darker printing and triangular markers. The platinum and 18K white gold Ref. 3970s
were also available with a black dial, and/or has diamond markers or white gold/platinum indices (the latter being much rarer).
There are a very small number of ref. 3970’s in 18K yellow gold with silver diamond dials; such watches are extremely rare.
Patek is also known to have produced diamond dials in both salmon and white. Again, Ref. 3970 with custom dials such as
the ones described is exceptionally rare. Hands: during production of the Ref. 3970, the hands of the watch changed slightly.
The earlier models (first generation) had leaf hands, whereas later models (second generation) had bâton hands.
It is not known when this change took place. One extremely rare variation on the Ref. 3970 has been seen with dauphine hands.
The Movements: Ref. 3970 was fitted with the 27-70 caliber throughout its entire production. Although there are no variations
in the caliber itself, the number system did change during the mid 1990s when it went from a six digit serial number beginning
with 875 to a seven digit serial number beginning with 304. Although it has less of an effect on value than dial or case variations,
an earlier serial number is generally considered more desirable than a later one. This Ref. was no longer featured in the catalogues as of 2005.