This may sound stupid, but it might have been cleaner with the soil removed…maybe?
I had a frantic call one time after I had cleaned a sofa. She said there was a dark band around the sofa and she wad totally pissed… I turned my van around and returned to the scene of the crime.
The area where the cushions hit the sofa had not been faded by the sun coming in the sliding glass door it was facing. The band was the unfaded area.
Food for thought and those new to the business..
May help someone.