Of course nobody really knows other than Jumbo, but it's not like people don't have their suspicions
I mean, we've seen the same level of often just insane team-wide performance from Gewiss, Festina, US Postal, Saunier-Duval, Sky, etc, all of whom have either been rolled up entirely or managed to sweep it under the rug and make people ignore it. I'm sure I'm forgetting some, and I didn't count the ones where I believe there were no actual cases in the end, but where teams are full of highly dubious figures (UAE the past years, Astana before their decline, Vacansoleil which was ridiculously good for one or two years, and so on).
It's impossible to know things for sure though, but if we can only have at least some small suspicions when we are absolutely sure....