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
Reorganization of the Senate - Its Complement Filled Up by Extraordinary Election - Admission to the Senate through the Quaestorship - Abolition of the Censorial Supervision of the Senate
For this purpose the governing board had, first of all, to have its ranks filled up and to be itself placed on a footing of independence. The numbers of the senators had been fearfully reduced by the recent crises. Sulla no doubt now gave to those who were exiled by the equestrian courts liberty to return, for instance to the consular Publius Rutilius Rufus,(12) who however made no use of the permission, and to Gaius Cotta the friend of Drusus;(13) but this made only slight amends for the gaps which the revolutionary and reactionary reigns of terror had created in the ranks of the senate.
12. Cf. IV. VI. Livius Drusus
13. Cf. IV. VII. Rejection of the Proposals for an Accomodation
Accordingly by Sulla's directions the senate had its complement extraordinarily made up by about 300 new senators, whom the assembly of the tribes had to nominate from among men of equestrian census, and whom they selected, as may be conceived, chiefly from the younger men of the senatorial houses on the one hand, and from Sullan officers and others brought into prominence by the last revolution on the other.
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Reference address : https://www.ellopos.net/elpenor/rome/4-10-sullan-constitution.asp?pg=21