here is the documentation of the 1976 coin with the proper explanations, there are no "error" on any of them, they are simply minted in different places with different dies. By the way there are more differences, which you can see in Cobra's documentation (in French) here:
https://varietes-2.000webhostapp.com/FICHE%20AFRIQUE/Tunisie/TUNISIE%201%20Dinar%20kM%20304.pdf
Ole