No idea as to manufacturing date for either set, and it is likely that there will be stock of the old ones in the supply chain for a while yet. However the telling point is the current ratings claimed and the CSA of copper inside. I see many cables of origin questionable that claim a rating but which do not have the copper inside to back it up. Often they are barely half the copper required, or have such poor quality that they break easily with only minor use.
The difference in both copper content and insulation in these cables is telling, the left one is far more likely to have broken strands working through the insulation. Double insulation is more to allow detection of failure of the outer layer due to wear and abrasion before the thickness of insulation left is insufficient to allow standoff to the test voltage to be safe. It does not offer any much more protection against manufacturing defects and in fact can cover them ad lead to a false pass. Ideally these cables should be tested for defects between each coaxial extrusion to ensure there are no defects in the inner layer, but I would guess the lower cost manufacturers are loathe to add this extra cost step and only do a final check if at all other than a visual check.
For my part I am looking at making my own, using a cable with a rating more commensurate to the required use. The last 3 pairs of short 4mm to 4mm leads I made are made from old cable and new connector ends, I have found a local supplier of some quite reasonable ends, that are reasonably strong and will accept a cable, while being stackable. They do cost more in materials, but are a much better item for my purposes. All I need to do is to get a source of good crocodile clip ends and make some.
