In Nov. 1960 Grünenthal (for the first time) inserted a notification into the Contergan instruction leaflet. The notification warned about nerve damage. However, the note stated that the nerve damage only appeared if the drug was taken over a long period of time and was also completely reversible after the intake of the drug was discontinued – which turned out to be wrong.
Source: Chronology of events provided by Beate Kirk, in: Der Conterganfall: eine unvermeidbare Arzneimittelkatastrophe? Dissertation. Greifswald 1998.