Tutte le date vengono date secondo il calendario giuliano in vigore in Russia al 1918. Could you translate it to English, please?
All dates are being provided based on the Giulian calendar which was used in Russia from 1918. (you wrote I assume “al” is a misspelling for “dal”).
First “date” means dates. Second date is the past participle of “dare”: to give, or to provide, in this case.