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
Attended by these and other able officers, Metellus presented himself in the course of 645 as consul and commander-in-chief to the African army, which he found in such disorder that the generals had not hitherto ventured to lead it into the enemy's territory and it was formidable to none save the unhappy inhabitants of the Roman province. It was sternly and speedily reorganized, and in the spring of 646.(12)
12. In the exciting and clever description of this war by Sallust the chronology has been unduly neglected. The war terminated in the summer of 649 (c. 114); if therefore Marius began his management of the war as consul in 647, he held the command there in three campaigns. But the narrative describes only two, and rightly so. For, just as Metellus to all appearance went to Africa as early as 645, but, since he arrived late (c. 37, 44), and the reorganization of the army cost time (c. 44), only began his operations in the following year, in like manner Marius, who was likewise detained for a considerable time in Italy by his military preparations (c. 84), entered on the chief command either as consul in 647 late in the season and after the close of the campaign, or only as proconsul in 648; so that the two campaigns of Metellus thus fall in 646, 647, and those of Marius in 648, 649.
It is in keeping with this that Metellus did not triumph till the year 648 (Eph. epigr. iv. p. 277). With this view the circumstance also very well accords, that the battle on the Muthul and the siege of Zama must, from the relation in which they stand to Marius' candidature for the consulship, be necessarily placed in 646. In no case can the author be pronounced free from inaccuracies; Marius, for instance, is even spoken of by him as consul in 649.
The prolongation of the command of Metellus, which Sallust reports (lxii. 10), can in accordance with the place at which it stands only refer to the year 647; when in the summer of 646 on the footing of the Sempronian law the provinces of the consuls to be elected for 647 were to be fixed, the senate destined two other provinces and thus left Numidia to Metellus. This resolve of the senate was overturned by the plebiscitum mentioned at lxxii. 7.
The following words which are transmitted to us defectively in the best manuscripts of both families, -sed paulo... decreverat; ea res frustra fuit,- must either have named the provinces destined for the consuls by the senate, possibly -sed paulo [ante ut consulibus Italia et Gallia provinciae essent senatus] decreverat- or have run according to the way of filling up the passage in the ordinary manuscripts; -sed paulo [ante senatus Metello Numidiam] decreverat-.
Do you see any typos or other mistakes? Please let us know and correct them
Reference address : https://www.ellopos.net/elpenor/rome/4-04-rule-restoration.asp?pg=42