Eric,
I cannot say for sure if the serial number shown in Plate 1504A is wrong or not. However I have documented several JUF back plates that have serial numbers below 50000 and one of them with serial number 545 is shown below.
Mun C W
Eric, here's that clock.
Mun C W
Mun, thanks very much for posting your low serial number and magnificent JUF clock. I have compiled some information regarding these low serial number movements that may help to define when these clocks were made. At this instant I have data for three of these including your clock, including serial numbers 300, 545, and 725. You mention that you have documented several back plates with low serial numbers, it will be very much appreciated if you could post what you have for discussion here, with photos if available.
My observations including your clock and serial number 300 indicate the earliest possible manufacturing date would be mid-May 1912 at about serial number 120000 when JUF made major changes in their movement construction and features that applied to all movements made after that date. These include:
1) The movement plate thickness was decreased by 0.4 mm from 2.4 mm to 2.0 mm.
2) Upper suspension bracket #10 was introduced and became the standard upper bracket.
3) The pediments were attached to the front of the front plate using the two upper movement post securing nuts instead of being held by screws to the top edge of the front plate.
These all would have been cost-saving measures at a time when the economy in Germany and Europe wasn't all that good and brass was increasing in cost.
I don't have photos of the clock with serial number 725 but have physically examined it thus these observations all apply as well.
A very interesting point regarding these low serial number clocks is they all have very elegant cases and until now none have been found with the common glass dome and spun brass base. Further, none of these cases are shown in the 1910 JUF 400-Day Catalog. However, the same type and design cases have been documented with seven other JUF clocks that have normal serial numbers. Based on the movement serial numbers three of these were made before WWI and four after the war including one that has Plate 1595 made in 1927-1931. It is believed that most of these low number clocks were made after WWI, however we need a lot more data before reaching a firm conclusion.
As to the question of why the low serial numbers, my opinion is that those particular clocks were made as a special order by a third party, as we have seen with all other 400-Day makers both before and after WWI. Unfortunately we haven't found any names yet but with more examples that may be confirmed.