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
It was thoroughly necessary to leave to the censors absolute control over the personal composition of the senate and the equites; for the right of exclusion could not well be separated from the right of summoning, and it was indispensable to retain such a right, not so much for the purpose of removing from the senate capable men of the opposition--a course which the smooth-going government of that age cautiously avoided--as for the purpose of preserving around the aristocracy that moral halo, without which it must have speedily become a prey to the opposition.
The right of ejection was retained; but what they chiefly needed was the glitter of the naked blade--the edge of it, which they feared, they took care to blunt. Besides the check involved in the nature of the office--under which the lists of the members of the aristocratic corporations were liable to revision only at intervals of five years --and besides the limitations resulting from the right of veto vested in the colleague and the right of cancelling vested in the successor, there was added a farther check which exercised a very sensible influence; a usage equivalent to law made it the duty of the censor not to erase from the list any senator or knight without specifying in writing the grounds for his decision, or, in other words, adopting, as a rule, a quasi-judicial procedure.
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Reference address : https://www.ellopos.net/elpenor/rome/3-11-government-governed.asp?pg=12