24 Feb '22:

Now the afterthoughts begin.

1) How to prevent insertions of narrow ones between any two numerals?

Possible solutions: 

a) Space the numerals regularly so an interpolated one will look crowded and thus fake.

b) Draw all numerals touching.

c) Formally require that any valid one have a half-character space on both sides.

d) Add an exaggerated serif to the one that indicates this distance.

(Gallery has been updated to reflect solution 1d.)