Installed 10.9 13A3017 on an external drive from one of the new MacBook Pros, then set it up based on "Creating Minimal Base OS Images for Restore or NetBoot/Netinstall Imaging." Installed Casper Imaging 8.72. Tested as a bootable hard drive on the new MacBook Pro, older MacBook Pro (late 2011), Mac Mini... The hard drive booted what I threw at it and opened up Casper Imaging - pointed at our server.
Did the clean up process and used the hard drive to create a netboot image using "System Image Utility" on a early 2013 Retina MacBook Pro running 10.9. (13A603) Placed the NetBoot image on a server and first attempted to netboot the older systems. It failed on them. Same image that booted them when on a hard drive... Netbooted the new hardware, and it worked!
So, the NBImageInfo.plist is what stopped the ability to netboot the older systems. Any reason to NOT edit the NBImageInfo.plist and add the older hardware?