Thanks Matt,
I just had a look in Control Panel and strangely the Kontakt Factory Library isn't there.
I possibly installed it in Windows 7 and then just pointed Kontakt in Win 10 to it although NA also seems to have detected it at some stage.
Win 10 Control Panel:
Win 10 NA:
In both Windows 7 & 10 I had all the drive letters matching for all of my hard drives and the "other" Windows SSD drive mapped to W:\. So in Win 7 the W: drive was the Windows 10 SSD and in Win 10 the W: drive was Win 7 SSD. Another story, but at some stage I had planned to "merge" the Kontakt libraries using a Win 10 library so that their location would not matter but it seems that Kontakt doesn't support this and requires an actual drive letter to locate specific libs.