The evidence that it is a welded and re-drilled fan is that the bolt holes are not in the correct radial position.
What appears to be the remanents original 3" holes on the painted side are in the correct radial position.
So, it is a rare fan in that it is a 4 rivet, though the ad could mislead if not carefully read.
The seller does not claim it to be an original 3.25" 4 rivet fan.
The seller does not claim it to be an extremely rare fan, only extremely rare fan blades [4 rivet]
The seller does mention that it has been machined, though does not specifically mention that this is because it has been welded and re-drilled.
So, probably still worth a good dollar being a 4 rivet, but would have been better to not have welded and redrilled it and to simply mention this as a possible mod in the ad.
There's probably a number of 3" 4 rivet hunters who are currently howling at what has been done here!