That's usually the data the BIOS was compiled and will be identical across all different computers with the same motherboard running that same BIOS version.
To get an idea of the date of manufacture of your actual motherboard you can look at the date codes of various chips on the motherboard. This is generally a 4 digit code, first two are year and second two are week. So 9433 is week 33 of 1994.
This isn't entirely accurate though as these components were probably manufactured at a different factory and sat in a warehouse for a while before they were actually assembled into a motherboard. So its a general idea of the age of the board. Some boards will have a datecode directly on the PCB which should be the most accurate idea of when the board was assembled but this isn't very common.
If you are squeamish, don't prod the beach rubble.