Sing, sang, sung

In linguistics, the Indo-European ablaut is a system of apophony in the Proto-Indo-European language. An example of ablaut in English is the strong verb sing, sang, sungand its related noun song, a paradigm inherited directly from the Proto-Indo-European stage of the language. All modern Indo-European languages have inherited the feature, though its prevalence varies strongly.

But, it says later, this frorm changed:

Consequently, the athematic verbs became a non-productive relic class in the later Indo-European languages. In groups such as Germanic and Italic, the athematic verbs had almost gone entirely extinct by the time of written records, while Sanskrit and Ancient Greek preserve them more clearly.

Using prefix and suffix modification became more populat before writing was common.   Their conjugation chats look similar, but they are reconstructed and match some ancient greek and sanscrit well. Active verbs had either an action completed or and ongoing action.  Verb suffixes were a or o.  Latin does indeed seem o be a dictionary format, the first effort of etymology to putt his all into a formal written grammar.