Eric, the lowest serial number in my data for this pendulum is 92355 made in December 1909 per my dating info, and the highest is 99909 made about August 1910. I suspect there could be slightly lower numbers for the "start" date, say as low as 91000 which is mid-November 1909 just after the DRGM was granted on November 12, 1909. However, I doubt we will find serial numbers higher than your estimate of 99999 as there were design changes made to the pendulum not long before that when pendulum 39 was introduced.
The first pendulum No. 39, which was made with the same DRGM number as the "Arrow" pendulum but not at all the same design, shows up at serial number 97195 and quickly displaced the "Arrow" pendulum. The transition period covers only about 2,000 clocks which would be reasonable considering they were making 12,000 annually.
There is also a DRGM 455721 granted to JUF on February 14, 1911 that describes a 4-Ball pendulum with a rating disc mechanism that appears to be the basis for pendulum No. 39, however that DRGM has not been found stamped on any pendulum so far. It now seems more likely that a modification was granted to DRGM 402658 that enabled the introduction of pendulum No. 39, but thus far we have not confirmed this. In any event, both pendulums were stamped with DRGM 403658. For pendulum No. 39 that lasted at least to November 1915 based on the original DRGM being valid for its initial three years and extended for another three.
One additional point for the record is that a significant number of No. 39 pendulums with the DRGM 403658 stamp have been recorded on clocks made up to 1923, but only a couple after that year. We don't know if this was due to JUF having over-produced the DRGM version of No. 39 before WWI and then just using them up after the war, or if there was some other reason. Another mystery to unravel.