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
In this way it became possible that, although the eligibility of plebeians had been established by law already in 333 for the quaestorship and thenceforward continued to be legally recognized, it was only in 345 that the first plebeian attained the quaestorship; in like manner patricians almost exclusively held the military tribunate with consular powers down to 354.
It was apparent that the legal abolition of the privileges of the nobles had by no means really and practically placed the plebeian aristocracy on a footing of equality with the clan-nobility. Many causes contributed to this result: the tenacious opposition of the nobility far more easily allowed itself to be theoretically superseded in a moment of excitement, than to be permanently kept down in the annually recurring elections; but the main cause was the inward disunion between the chiefs of the plebeian aristocracy and the mass of the farmers.
The middle class, whose votes were decisive in the comitia, did not feel itself specially called on to advance the interests of genteel non-patricians, so long as its own demands were disregarded by the plebeian no less than by the patrician aristocracy.
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Reference address : https://www.ellopos.net/elpenor/rome/2-03-equalization-orders-aristocracy.asp?pg=12