Usually on Sudanese coins the "reignal year" repeats the accession year, but some show the correct accession year of the Khalifa, a few refer to the accession year of the Mahdi, some have errors confusing "5" and "0", and some ... some will drive you crazy, if you try to understand them.
In these times and this area there were not only artists working in the mint of Omdurman.
On Darfur coins the accession year is usually "17" regarding the accession date of Ali Dinar, but sometimes occurs also "71", the accession date of Ibrahim Muhammad Hussein al-Mahdi, his grand father, the last Sultan of Darfur.
So the thumb rule is: In the hardest times in the poorest areas nobody cares about correctness of letters and numbers on coins.