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
The extent and the comprehensive effect of these distributions are attested by the numerous arrangements in the Roman art of land-measuring that go back to the Gracchan assignations of land; for instance, a due placing of boundary-stones so as to obviate future mistakes appears to have been first called into existence by the Gracchan courts for demarcation and the land- distributions. But the numbers on the burgess-rolls give the clearest evidence.
The census, which was published in 623 and actually took place probably in the beginning of 622, yielded not more than 319,000 burgesses capable of bearing arms, whereas six years afterwards (629) in place of the previous falling-off(2) the number rises to 395,000, that is 76,000 of an increase--beyond all doubt solely in consequence of what the allotment-commission did for the Roman burgesses.
2. Cf. IV. II. Ideas of Reform
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Reference address : https://www.ellopos.net/elpenor/rome/4-03-revolution-gaius-gracchus.asp?pg=3