I'm not sure if it would matter if they were really inaccurate if the ship used the same sandglass and rope. I've read about the shipping log -> world map work [1] where it details that the speeds/distances for a given group of boats had different errors which the gentlemen developed a technique to resolve.
[1] https://priceonomics.com/a-map-of-the-world-made-from-shippi...