u/basis-tranquilitatis

I've heard this claim repeatedly that pre-Carolingian Latin wasn't simply read out loud by "applying sound changes of the local dialect to the text", but by also changing the wording in several contexts. For example they supposedly substituted complete prepositional phrases for nominals when the case they were in had died out from the vernacular language. So the word {casarum} could've been read out loud as "de cásas" or even as "de įllas cásas" instead of simply as "casáro".

Is there any concrete evidence for such practices?