[Brightcolours]

Correction of distortions also affects the effective focal length (or angle of view, more precisely) by stretching and cropping the image. In the case e.g. Oly 12-40mm f2.8, is the 12mm the FL before or after the software correction of distortion?

 

I tend to belive it is the FL after the correction since the correction is done automatically but I want to check.

The focal length does not change. Uncorrected lenses or under corrected lenses just show a wider view (one can see uncorrected fish eye lenses as lenses with a LOT of barrel distortion). So, uncorrected it just will give a wider view than a corrected lens with the same focal length.