I've been running a triple-boot MacBook (High Sierra / Windows 7 / Snow Leopard) for a long time, and it's been working fine.
I've recently bought a new (to me) MacBook Pro (15" Mid-2012 2.3gHz) and have replicated the boot drive of my previous MacBook (core2duo 2009) onto an SSD which I've fitted into it.
Well, High Sierra boots fine and I've been working on it for a few months, but neither Windows nor Snow Leopard will boot.
Both are seen in the EFI boot-loader and both partitions are mounted and visible in High Sierra.
Like, uh, what's the deal?
Is there some kind of 'gotcha' with it being a 'newer' machine?