For the holiest Torah texts, including the 5 books of Moses, a design was used which didn’t allow any mistakes at all. If the Sopher (the writer of the Torah scrolls) made one mistake he was forced to throw out the whole scroll. A different ink was used each time the name of God was written. A Sefer Torah scroll includes 304,805 letters and if a single one of these had been written incorrectly, the whole scroll would be invalidated. This means the scrolls remaining today have had the same design for the past 2000 years
