My understanding of the code is limited. But I can see that the description used for two tags is misleading.
Text visible on 4b0b67b
States..
“GB-WLS:nsl_restricted”: “National Speed Limit, built-up area with street lights”,
“GB:nsl_restricted”: “National Speed Limit, built-up area with street lights.”,
The “built up area” needs to be removed and changed to read (eg) "“National Speed Limit, for roads with street lights.”
This would mean the description is in line with the wiki Key:maxspeed:type - OpenStreetMap Wiki
The default 30 mph limit in the UK is dominated by urban areas, but this defualt limit is created presence of street lights which also occur in rural settings.