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
Now as this field of general powers was thus doubly occupied, the one consul in reality remained at the disposal of the government; and in ordinary times accordingly those eight supreme annual magistrates fully, and in fact amply, sufficed. For extraordinary cases moreover power was reserved on the one hand to conjoin the non-military functions, and on the other hand to prolong the military powers beyond the term of their expiry (-prorogare-). It was not unusual to commit the two judicial offices to the same praetor, and to have the business of the capital, which in ordinary circumstances had to be transacted by the consuls, managed by the -praetor urbanus-; whereas, as far as possible, the combination of several commands in the same hand was judiciously avoided.
For this case in reality a remedy was provided by the rule that there was no interregnum in the military -imperium-, so that, although it had its legal term, it yet continued after the arrival of that term de jure, until the successor appeared and relieved his predecessor of the command; or--which is the same thing-- the commanding consul or praetor after the expiry of his term of office, if a successor did not appear, might continue to act, and was bound to do so, in the consul's or praetor's stead.
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Reference address : https://www.ellopos.net/elpenor/rome/4-10-sullan-constitution.asp?pg=33