Many thanks Jim - your explanation fits well and goes a long way to explain why I was unsure about these. I was under the impression that these were 1880-1900, so I had not thought of more modern steel. It is very difficult however to see the difference between this and trade blade steel in terms of quality. Flexibility seems pretty much the same as a trade blade, so I suspect it is not leaf-springs but something else. I've attached a couple of pictures of a takouba that I believe is made from leaf-spring steel. It has rather a different feel to the blade (more rigid) and a more course structure to the steel (although this is a difficult thing to appreciated from pictures)
As to the different conditions of the blades I suspect you are right about storage. These came in from the same source as the probably 14thC takouba currently being discussed on the forums. Two teleks also came with these, both rusted into the scabbards, the scabbard from the rusty kaskara is in pretty small pieces, possibly as a result of removing the blade. I think that some of these got wet at some point in the not too distant past, and the takouba was lucky not to be one of these. So on the plus side I would say that there are two types of oxidation present on all of these - new and old. The old looks like nice black patina (you can also see this on pics of the crocodile hilted one, under the langet), the new is fresh and active rust. I guess that patina could have developed over the last 50 or 60 years, if that is the age we would put on these, and that the better kaskara was cleaned whilst the other was left untouched?