Although South Bend have comprehensive records of their lathe production (and can quote an exact dispatch date for almost every machine ever made) it is possible, thanks to the efforts of Geoff Swayze, to calculate an approximate date of manufacture - to plus or minus one year or so - if you enter the serial number (stamped at the tailstock-end of the bed) raised to the power of 0.0059 then multiplied by 1812.
The procedure is as follows:
On a scientific calculator (the one with any version of Windows will suffice) enter the serial number, say 84243; then hit the X^Y key (X with a superscript Y); type in 0.0059 then hit the "=" key followed by the multiplication key (*) followed by 1812. You should obtain 1937.4 which is within one year of the real date of manufacture, 1938.
Until a change of policy in 1947 - and a production total of approximately 186,500 lathes  - South Bend used a simple sequential numbering system but after that the serial numbers were broken down between different types of lathe with numbers assigned sequentially within a group.  Adding the highest serial number seen in each category post-1947 to the pre-1947 numbers gives a total production of just a little over 330,000 units; however, by the 1970s South Bend's range was very limited and most of the lathes produced during the last 30 years of the 20th century were the eternally-popular model 10K - a direct descendent of the original 9-inch lathe of the 1030s..