Boot Camp on External Drive

I replaced the hard drive on my MacBook Pro with a solid state drive about a year ago. The SSD was smaller so I didn't include a Boot Camp partition on it. I populated the new SSD using Time Machine restore, so only the Mac content was transferred. Since that time I have upgraded the MBP to El Capitan.

Since there was nothing wrong with the old hard drive, I put it in an enclosure to connect via USB. Now, when I connect the old drive, I can see both the Mac and Boot Camp partitions, but when I look at the alternate-boot options with the USB drive plugged in, only the Mac partition shows in the list (and is bootable).

Is there any way to make the Boot Camp partition on the external drive bootable?

Failing that, is there a way to retrieve the Windows license that is on the Boot Camp partition on the external drive so that I can use it elsewhere?

Walt