Not familiar with the bolts on a VW sump, never worked on one. But on a Ford Kent engine the rear 2 bolts are impossible to remove (and see) with the engine and gearbox in situ. On a Caterham its not unknown for the sump to get damaged (mine has 3" clearance, many have less) and many first timers would remove the obvious bolts and then try removing the sump with the 2 inside the bellhousing still in situ. The really insistent amongst them would then resort to the chisel or screwdriver in the belief that it was the sealant that was stopping it coming off. result was a destroyed sump at best, destroyed rear bolts and damaged block at worst.

Wonder if the sheared bolts on this VW have been caused by a mechanical marvel having all the gear and no idea. Should have gone to spec savers.

On the Caterham the manual told you a simple way to enable removal without splitting the engine and box. Before fitting the sandwich plate between the engine and gearbox make 2 cuts that would enable the lower part to be removed by taking out bolts, then the 2 sump bolts are easy to see and relatively easy to access. All the plate does is prevent road debris entering the bellhousing. One enterprising fellow omitted the plate, he thought he knew better than Ford, big mistake. Cost him a new engine.

Possibly the two hidden bolts at the rear of the sump, as shown on this video from 2 minutes in. Not easy to access for removal if they have sheared.

Not easy to notice either ? Perhaps someone applied a spanner and zealously overtightened them. Why would they do that ?

Human error? Or tried to remove with the wrong tool, or pulled the sump without removing them maybe. They say it was a problem with the car being old. I can't prove anything.