It was discussed long ago. I can talk about that because I know Latin and Russian is my native language. Old Russian as well as Serbian for example had more past tenses, it had Vocative case, the verbe 'to be' in Present. The Past tense was formed by the verb 'to be' in the Present + Past Participle - дал есмь, дал еси, дал есть and so on. So it was closer to Latin than the modern language.