You are correct that there is no concrete evidence, but look at what happened in December when AMBS changed its CUSIP number and name. Our German friends told me this forced the MMs on the BBSE to temporarily delist the company when it went into effect, and when that happened the PPS surged.
You don't find it hard to believe its not a coincidence AMBS recently got suspended from the BBSE and now its on the FTD list? The same broker selling shares on OTC was selling shares on BBSE...
Do your own DD and do not trust anything without verifying it yourself.