Just a couple more thoughts about these swords. I mentioned that I thought the tang might give a clue. The rusty blade with deep patina came in wooden hilt with a very worn grip. There is distinct evidence that this is wear and not water damage. The wood itself is old dry and fragile. What I think might be significant is that the hilt did not utilise an iron peg passing through the tang, which according to this thread
http://www.vikingsword.com/vb/showthread.php?t=13638 is the purpose of the hole. So my thought it that this has been re-hilted at some time, but if so how did this happen and the current hilt get into this state if the blade is only 50 years old? I also noticed that the blade itself has been sharpened and shows a distinct narrowing in the fiths 3 & 4 from the hilt - again not something I'd expect to see on a young sword that as been left in an outbuilding.
I think the key issue here is the 'comet'. Do we really know that this was not found on kaskara before 1960? The marks themselves are deeply inscribed. I've rubbed gently at the rust with a scotch-brite pad and I can now see that there is a difference in the marks between the two blades. The rusty blade mark is not identical e.g. that if we imagine the mark is a figure carrying a staff or flag, then the flagstaff on the other mark extends quite a way above the head of the figure in the rusty version and barely at all on the clean version. There is a difference in the rectangular mark at the top of the head too. I've tried to capture this and the blade wear in the pictures below - but more cleaning will be needed to bring the mark out clearly. To help I've traced the marks visible from this angle. The cross-hatching visible on the clean blade is also present on this blade but it requires a different angle of light to bring it out.
Another possibility is that the mark has been added to an earlier blade, but I don't know whether this is likely. Not all trade blades seem to carry stamps though, and not all have been added to by native stamps, so perhaps this is possible but unlikely.
So I agree with Jim that more research on what this mark means and where and when it came from is needed, but I'm not yet convinced that these swords are a young as suggested.
Great fun trying to figure this out though
Chris