We are a Capel Rug Dealer.. I'll check with our rug sales manager for info, but you are correct that there is not much you can do with the tufted rugs, you could attempt to odorcide bomb it or similar but my guess and most ruggie's would agree that the odor is usually quite permanent. There are several ideas on why the latex is is off gassing but it comes down to the fact that a majority of the foul smelling rugs are made with cheap labor over seas with no quality control and as a result inferior quality of latex in the backing. One theory is south asia's humid climents have caused bacterial growth in batches of the latex. Just like a urine problem in high humidity, the cleaning may have reactivated the foul smell or amplified it.
But its also not a bad idea to investigate if there are possible pet problems with the rug or others. Generally these rugs smell from the get go.. we have had to replace a few as a result when they came in.
Either way best of luck on this one!