Yes, I think the distinction between valid reason and a plain no is important. From my understanding the wife cannot refuse her husband without a legitimate but if she has a valid reason such as illness, being tired and physically not able etc than the husband has to respect that and not force her. Think of it this way Islam is not a harsh religion why would a husband be allowed to force something upon his wife. It doesn’t sound logical.
As far as the original question, Yes i think it probably happens and i’m sure sometimes the women herself may not realize it happened. I think in the desi community older generation might not even understand the concept of marital rape. Anyways I think husband and wife should respect each others needs and wants and compromise when needed.