These projects employed skilled journey men (level between apprentice and master). At some point they then traveled to work on the next project, spreading the know-how. Once something was working, it was often copied as modifications were risky.
To add to this: those were highly sought after specialists with a lot of privileges. This had consequences that sound strange to us nowadays.
Stonemasons were heavily involved in medieval diplomacy, since everybody in power needed them to build or repair fortresses. They could travel freely between kingdoms that were at war with each other and exchange messages between the respective rulers.
