The article https://en.numista.com/catalogue/pieces1748.html
has the year distribution:
Year Mintage
1979 25,001,000 with edge lines flanking "10"
1981 with edge lines below "10"
1981 40,000,000 with edge lines flanking "10"
1981 2,670 ESSAI نموذج
Should be
Year Mintage
1979 25,001,000
1981 40,000,000
1981 2,670 ESSAI نموذج
Due to technological process of minting, the images on the edge appear on the flank before the images on the sides. That is why their position is random, and as a result this difference is neither error nor variety.
The removing of the extra line does not bring to problems with the collections of swappers: all the coins will be united under 1981.