Hi Dave
Without knowing what the source of mal-odour is, nobody will be able to give you a definitive answer.
If it's a wet sheep/wet dog problem, then time, boosted by a blower and ventilation is the best cure.
If it's a cat problem the soiling will require specific attention. Also, it could be, or also be, on a vertical surface and has been reactivated by the increase in humidity of cleaning.
Sour milk and other food should be treated as a specific problem, not general.
Although I don't use it as a "front line" cleaner, I find that M Power (I presume that Nemesis will be similar) will clean and have a beneficial effect on general carpet/room mal-odours.
IMO, the problem described is beyond the scope of Lemon Refresh.
Safe and happy cleaning

Ken