Stacking difficult terrain

[Ravingdork]

Came up in a game last night. If you're blind, and thus treating everything as difficult terrain, but are also working your way through actual difficult terrain, are you furthered slowed? Perhaps treating it as greater difficult terrain?

[Fuzzy-Wuzzy]

Since I can't find a relevant rule, I argue that they do not stack because if they did you'd want to allow arbitrary amounts of stacking by making it condition-like: difficulty 1 terrain (normal), difficulty 2 terrain (greater difficult), difficulty 3 terrain, etc. I haven't taken the time to ponder this reasoning much, let me know what you think. :-)

[Chrono]

By rules it doesn’t stack unless it is explicitly said to, or increase terrain difficulty unless explicitly said to - like how getting darkvision from both ancestry and heritage doesn’t give greater darkvision (but getting low-lighf and a feat that gives low-light usually does stack to dv due to feat wording). You could possibly rule it as also being uneven ground for that character, since they can’t see to navigate around what is causing the terrain to be difficult - but tbh being blinded is punishing already.