Please note that Mommsen uses the AUC chronology (Ab Urbe Condita), i.e. from the founding of the City of Rome. You can use this reference table to have the B.C. dates
From: The History of Rome, by Theodor Mommsen
Translated with the sanction of the author by William Purdie Dickson
Government of Cinna
Along with the reign of terror came the -tyrannis-. Cinna not only stood at the head of the state for four years in succession (667-670) as consul, but he regularly nominated himself and his colleagues without consulting the people; it seemed as if these democrats set aside the sovereign popular assembly with intentional contempt. No other chief of the popular party, before or afterwards, possessed so perfectly absolute a power in Italy and in the greater part of the provinces for so long a time almost undisturbed, as Cinna; but no one can be named, whose government was so utterly worthless and aimless.
The law proposed by Sulpicius and thereafter by Cinna himself, which promised to the new burgesses and the freedmen equality of suffrage with the old burgesses, was naturally revived; and it was formally confirmed by a decree of the senate as valid in law (670). Censors were nominated (668) for the purpose of distributing all the Italians, in accordance with it, into the thirty-five burgess-districts--by a singular conjuncture, in consequence of a want of qualified candidates for the censorship the same Philippus, who when consul in 663 had chiefly occasioned the miscarriage of the plan of Drusus for bestowing the franchise on the Italians,(8) was now selected as censor to inscribe them in the burgess-rolls.
8. Cf. IV. VI. Discussions on the Livian Laws
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Reference address : https://www.ellopos.net/elpenor/rome/4-09-cinna-sulla.asp?pg=21