Love this question. It looks like all of the answers so far give us the release date of the BIOS applied to the hardware. If you update your BIOS, I would expect this date to change, so I started to try to solve the Hardware Manufacture date, for the system board.
I just did some digging into my Thinkpad’s smbios with this query:
q: (name of it|"", names of values of it, values of it) of structures of smbios
It’s an interesting read.
Manufacture Date of the System Board - is nowhere to be found!
To get my manufacture date, I had to go to a Lenovo Website:
https://pcsupport.lenovo.com/us/en/warrantylookup#/
and enter my system’s serial number, which I did.

Looks like that March 07, 2019 date is nowhere in my SMBIOS structures.
q: (name of it|"", names of values of it, values of it) whose (item 2 of it as string contains "2019" or item 2 of it as string contains "2020") of structures of smbios
A: bios_information, vendor, 06/20/2020
A: bios_information, bios_version, 06/20/2020
A: bios_information, bios_starting_address_segment, 06/20/2020
A: bios_information, bios_release_date, 06/20/2020
A: bios_information, bios_rom_size, 06/20/2020
A: bios_information, bios_characteristics, 06/20/2020
A: bios_information, system_bios_major_release, 06/20/2020
A: bios_information, system_bios_minor_release, 06/20/2020
A: bios_information, embedded_controller_firmware_major_release, 06/20/2020
A: bios_information, embedded_controller_firmware_minor_release, 06/20/2020
A: bios_information, , 06/20/2020
Does anyone else know a trick to get the Manufacture Date of the System Board locally on the windows (or linux) box without using an external website lookup with the vendor?