“That doesn’t necessarily mean that he knew how to get blue dye from the murex.”
This was probably said 3 years ago, but Rav Herzog z’tz’l was convinced that the Murex was the right animal but that the dye was indeed blue. Rav Herzog z’tz’l died in 1959 but the rediscovery of how to get blue dye from it was not until over two decades later.