You do need an updated bios on the older motherboard to support kabylake.
Only if the the motherboard was manufactured prior to the Kaby Lake supportive BIOS version.
Doesnt matter when the motherboard is manufacture. If the manufacturer doesnt implement a kabylake supporting bios still wouldn't work out of the box. There is only one way to know if or when the latest bios on the website has been added. When people who purchase the motherboards report the bios version that comes with their board. Even then there is no absolutes.