The table below with the serial numbers and years has be compiled from many sources and I believe it to be reasonably accurate, However, no table like this can be completely accurate because Elgin didn't produce watches in sequential order.It was very common for groups of watches to be set aside and finished months, years, or sometimes as much as a decade later.Obviously, these later cases can't be related to the movement serial number.
Earlier wrist watches are often similar to pocket watches.
The reason that the movement and case serial numbers are unrelated is because up until the 1920's, almost all American watches were sold separately from the watch cases.
High volume watches will tend to be closer to the date listed, while expensive, high quality watches will tend to be the ones that have misleading dates.
New models of watches may be released before or after these general dates.
If your watch has a letter prefix, you must first replace that letter with the two digit "millions" value from the following table.
For example, H632161 would be converted into 47,632,161 and N7193 would be converted into 48,007,193.
Elgin originally started out with just a number, but in the late 1930s they started to use a letter prefix on some of their serial numbers.
Even later in the late 1950s, Elgin phased out the use of serial numbers.
The jeweler would then put the movement and the case together.
With only a few exceptions, the watch companies and watch case companies were completely unrelated business.
In addition, watch cases tended to wear out much quicker than the watch movements.