That is all really useful thank you for the responses. As I said I'm no bladesmith so I appreciate your patience.
I can supply a little more information. The shorter kaskara tang is 100% in line with the ´typical form. This was a particular sword type that uses a pin through a wooden (usually) grip to secure the blade. The pommel has no structural function but is just a leather disc to stop the hand slipping. I recently disassembled 6 of my swords and the form of the tang was the same with a seam up the middle where to me it looks like the metal was folded over then hammered out again. These were 1 18th century, 3 19C and 2 20C.
The blade itself does vary with age. The 18C has a more rounded profile, and all are slightly thicker towards the base of the blade. I see no hammer marks on the blades (which do occur on some blades from the area). Old texts refer to Hausa smiths as mounting the blades and making the fittings, but not creating the blade itself. My ideas here have been considering 3 possible sources for these mystery blades:
1) Locally produced from imported or locally sourced steel. If this was done anywhere it could most likely have been Kano, and then traded via the trans-Saharan trade routes. I think that this route is unlikely since to make a blade like this I understand from your replies that you would assume at least the use of a rudimentary form for mass production, and to my knowledge there were no trip hammers or water powered tools in use in sub-Saharan Africa at that time.
2) A almost finished blade ready to be adapted to local mounts, from Solingen traded via Alexandria/Cairo moving South-west. Here my worry is that all the Solingen blades I own have a different profile and colour to the steel (lighter colour than the 'mystery' blades). This could easily be because the steel sourced was different and different makes produced different blade qualities, but it is noticeable and consistent.
3) Italian blades - here I know that Tuaregs often had Italian bladed daggers from Tunis, traded south. It may be that the sword blades were from the same route but were unmarked and therefore it was not noticed that they were also Italian.
Your replies are extremely useful because from this I learned that the blade itself could feasibly have been mounted by local smiths, hence the poor workmanship, and that due to the softer tang this local refitting is quite possible. The dukari (half moons) could also be stamped locally (cold) either by local smiths (here I suspect this requires a very good stamp so maybe not), or a middleman who imported the blades applying the dukari and then selling them on.
For European imports the flatter profile of the blades might give a hint. I believe drop-forging appeared aroung 1860-1870 in Solingen at least, so mass production as described by Frosty would have been an option from this point on.
Wherever they came from I believe it points to relatively mass produced 'blanks' with the fitting adjusted to the takouba or kaskara as needed.
Btw 1950s kaskara were produced from lorry or Land Rover leaf-springs, and entirely locally. Unfortunately I do not have a bone-fide example of one of these to compare to.
I attached two more images - one showing this form of tang, the other being (I think) from Solingen showing a process of cutting to fit the kaskara needs. There is no 'folding' at the base of the tang on this one, so no mystery here what was done.
Thanks again for your help and patience.
Chris