I understand it comes across as jingoistic, but truly Sanskrit grammar and pronunciation hasn’t changed since Pānini. The word Sanskrit itself means “constructed” and there was a rigorous effort to prevent ambiguity.
Likewise, we have older information on pronunciation as well in the Pratishakhyas.
Ancient Indians cared a lot about accurate pronunciation, especially for mantras where the thinking was that without correct pronunciation, the mantra would not work. Picture the Harry Potter "wingardium leviosa" scene.
Modern don’t actually hew to the prescribed pronunciation for certain letters, but it’s certainly specified by Panini.