[Tagging] Historic road numbering?

[Philip Barnes]

Is there a means of tagging the old road numbers for a road that has
been declassified?

Sometimes you are not in a hurry and just want to go the old way, the
way people went before bypasses, motorways and interstates.

Something like:
highway=secondary
ref=B5478
ref_historic=A49

or
highway=tertiary
name=Leicester Road
ref_historic=A46

In both cases, the first two tags are existing tags.

I am struggling to even find the most famous of all, Route 66.

Thanks
Phil