I can in to this at World Bank HQ about 10 years ago. The construction company was going to have to replace 30,000 sq feet of carpet because of one hallway of about 500 sq feet. Someone had already done the solvents with truckmount rinse. It had been bonneted with a solvent shampoo and one clown tried HOST

. Nothing had worked and ot just kept wicking back. I rinsed it with cold water &
Prochem all fiber rinse to get all the chemical residue out and set up two blowers. Went to "lunch " for two hours. To solve the issue I encapped it with Cobb encap with protector. Zero issues and a huge check. They just recently replaced the carpet and it had a normal life cycle.
Why that worked ? Ask Larry, I never figured it out . Honestly it was a shot in the dark, just trying what hadn't already been attempted. Kind of like when rust remover takes out the ink that nothing will touch.