Agreed, welding a tempered die would completely ruin the heat treatment of the die. I was a machinist for years and worked with hundreds of different dies. I have also wire welded hundreds of parts to be put back into service. There is no stick or wire welder with thin enough wire to patch a die. I am not being disrespectful but this comes from years and years of working with such things.
here is some more welds. I know you guys know this. but see when you get a die chip. it leaves a hole in the die. so what the mints have been doing is repairing die chip holes plus some deformations. they also use the welds to strengthen and make certain edges harder. we have done a lot of that. when we were pressing steel. there is always wear points weld can be used to strengthen them. I know the welders here will know that. we also used the same practice on bulldozer blades, excavator buckets and excavator rock hammers. all we were trying to do was make the attachments last longer. that is the same idea at the mints with there dies.
ok here is a coin a Jefferson with a mouth repair. I have the coin that also show the large hole. so yea they have been doing this for a while. I mean all the mints. Denver philly. and Seattle, as well as the Royal Canadian Mint in Ottawa and the one in Winnipeg