Since I have been called forth I will state that I side with Bert.
Everyone needs to consider that a company , even if it is making a change, will use up materials and not just throw them out. Buck has to guess when this occurrs on how many warranty parts will be needed in the reasonable future. That along with reqular production will then end a production parts run and begin a "new and improved" production method. I would hazard a guess, and Mr. Hubbard can say I am wrong, that no older blades still exist if a 300 from that era needed a replacement. You would likely be offered a complete current model replacement or a repair using new steel. ( Wonder how that is going to work with the discontinued 309 and 305, You will likely be offered a new, other model, knife of equal value.)
All that said, you can see how it is not easy to say to even a six month period when a production method changed without looking at factory records to see when it occurred. And as per Mr. Houser, the move to Idaho left some holes in the historical record as records were lost to the dumpster gods. I have heard several people were visiting that dumpster daily for a short period.
Various people have recorded various dates for the beginning and end of the 425M era. I will go with a quick beginning when Buck took over the actual production of the models 301,303, 309 and 305 in very late 1985. Some (few) will say BUCK, U.S.A., be made by BUCK but have no date code and be 425M. In 1986 Buck introduced a new design in the shield. The round ended BUCK shield that was ink printed and can wear the ink off. Along with this started the beginning of the new generalized date coding system. So lets say 425M started in 1986 with blades marked < . 425M carried the load for the 301,303,309 and 305 till a gradual change to 420hc occured in the 1989/1990 (V and X ) at different times with the different models. Lets all just tell folks when they went back to the knife, bolt and hammer logo they quickly switched to Bos 420HC. During these events Camillus was still contracting the other models (307,311, 313 etc.) and they were hafted with Camallius standard steel. Usually a 420 steel made by a non-Buck contractor, just regular Camillus knife steel. As a busy time for the BUCK company this era was when Paul Bos moved in with Buck and heat treated all their blades along with some side contracts of his own.
More details than you wanted but knowledge is mental power. 300Bucks
