About ten years ago Richard Evans and I sent a number of reeds for hardness testing. Just from memory there were two Lach reeds, two Jeffries, two Wheatstone. The hardest was a Wheatstone but the other Wheatstone was relatively soft. One of the Lachenals was quite hard though not as hard as the hard Wheatstone, the other was soft. Both Jeffries were relatively hard. Having said that, the role of hardness in a reed is not well understood by me.
The difference in tone between vintage brands is better explained by wood choice and design, and by the clearance in the reed/frame gap, than by steel composition. I suspect given all other factors being the same, all relatively hard steels would produce much the same sound. Steel choice might contribute to response however. Brass produces a different sound but this can be explained in terms of stiffness and tip speed.
I suspect duplicates of old steels would be hard to find. Two factors were at work. 1) all subterranean ore bodies are different in their composition. 2) The big cost in steel production can be finding an economical way of bringing coal and iron ore together. The spot on the Severn River where both coal and iron were found in the same cliff face substantially kicked along the industrial revolution. A child of this equation is that early industry tended to use only one ore source, hence a steel factory could be putting out a unique product. Today ores are blended to create many different alloys.
It is hard to imagine Jeffries used Swedish steel for no real reason. It must have been cheaper, or made a better reed (in his opinion) or created a PR opportunity ("reeds made from finest Swedish steel!"). This last would be easy to disprove if period advertisements were available.
Spotting a Lach reed in a Jeffries can be difficult because the steady state sound comes from the wood and the design. The clues are in the response and whether the reed generates more upper partials from a close reed/frame gap. The effect of upper partials on our ear is different to lower ones. The combinations of lower ones contain much of the character we recognise as "fruity" or "nasal". I feel tempted to describe upper partials in terms such as edginess, cut, or annoying buzz. If the concertina is designed to have a lot of upper partial absorption then this difference may be hard to hear but you will feel it.
I find a file lasts about 1.5 concertinas, so 90 reeds. After that it is blunt and you have to use too much force. I always know when I held off too long before changing files; the first reed with the new file becomes quickly too thin and has to be discarded.
Thanks for your experiences Greg, I share your wondering how much crossover there is between hardness and resilience. I use the word stiffness for resilience. Every time I have ventured into this area it has become very complicated very quickly and I retreat in favour of more immediate progress. (Any moment now someone is going to use the term 'Young's modulus of elasticity'. http://en.wikipedia....Young's_modulus
Sorry I became discursive, off now, I have wood to split and reeds to make.