[Jim McDougall]

Triari, actually the thumb ring example was one of the two posted by Keith,
mine is the rather worse for wear one with the guard detached from pommel due to corroded metal. But thank you for the kind words.

As you note, the thumb ring feature is typically a Continental convention, and uncommon for English swords. However these sometimes occurred on hilts from northern Europe, i.e. Netherlands, which would put them in the conduit of swords and blades going into Great Britain. The groups of families in the border regions in north England known as Border Reivers were quite diverse in their allegiances, fashion, arms etc. Their weapons even included schiavona and many Continental arms forms.
As you note, such features were well known in incidental cases, the Cromwell instance for example.

The new rust circumstance might well have been from a change in the environment with the weapon moved into a new context and out of its original setting. This type of difference in the corrosion or deterioration of a weapon such as deep pitting on one side, less on other is an example.

The so called cabalistic motif on blades seems of basically European popularity which situated in Eastern Europe with astral and occult symbols, devices along with religious motif etc. These conventions with British sword blades seem to have evolved from 'hunting swords' in mid to late 17th through 18th c. which had to do with talismanic properties. French blade engravers in Nantes also were source for many of these types of motif, prompting imitation in England.

The Islay 'thing' is something only super-sleuth Keith could have found as he has explored British sword making as few others, and found I believe that there were makers of mortuary style hilts on Islay. There is virtually nothing known of these kinds of sword related industry in the Isles, so I too would like to learn more.