https://www.bobswatches.com/rolex-blog/watch-review/1665-double-red-sea-dweller.html

The Double Red SeaDweller (DRSD) was produced for approximately 10 yrs from 1967 to 1977 with serial number range 1.7 to 5.1 million. There were four different dial variations made in the regular production model with three different case back configurations.

The early version and the most rare is the Mark I dial on a patent pending caseback. These were made in the serial number range of 1.7 to 2.2 million. Mark II dials have also been seen on patent pending models. Patent pending Mark I watches command a pretty significant premium and some have sold for over $100,000.00. Mark II patent pending are also very desirable watches by collectors.