I don't think that the "brushed under the carpet" comment is fair. The company reported it, immediately they knew the details and they discovered the details in a timely fashion - that is, they were following their correct procedure.
The AAIB did comment that the original filed ASR didn't quite describe the extent of the event - but without access to the text nothing can be said on how "under reported" it was. The aircraft itself wouldn't have suffered any damage from the underspeed.