david weaver
Years ago, I had a couple of the LN sash mortise chisels (a2) and the Ray Iles mortise chisels (D2).

Both held their edges well.

I've subsequently bought older chisels (only out of curiosity, and because they were cheaper). I. Sorby oval bolstered, and they are about as hard as the LN and RI chisels, and their edge holding is similar.

A quick rub of the edge on any of these after several mortises (like 30 seconds worth) and nothing more is needed for hundreds of mortises, so I've never had to do a significant reset on any of these chisels and can't really say what would happen if someone set them all to 25 degrees and drove them through a louisville slugger with a hydraulic press.

I like the I. Sorby chisels a little better in use, they don't form a wire edge. It's insignificant in this case, to say the least.

Bench chisel work at angles people would like to use here in the states once they're further along (mid to high 20s), the above would probably be different (and it's highly dependent on hardness and quality of the steel and heat treatment).

Shepherd's A2 iron was at least as hard as any of the other ones I had. It was the worst iron I have ever seen by a long shot. No clue why (bad stock? bad heat treat?). Things came out of it in gloms. I sold the plane because the cap iron that came with it didn't fit other vintage parallel irons, and at the same time, other cap irons didn't fit in the shepherd plane because they saw fit to make the adjuster cup much different in size and depth than any other infill I've ever seen - nothing compatible.

Figuratively a caterpillar bulldozer of a plane with a briggs and stratton motor that couldn't be changed out for a diesel.