There was some degree of standardization. Especially for important legal and religious texts alteration, even if accidental, was considered a sin/vice.
Scribes very often simply had to produce 1:1 copies of existing texts. So the standard was right in front of them.
"Vamos a playa" by Righeira carries a lightweight, upbeat tune that vacationers might hum on the way to the beach. But the Spanish lyrics reveal that it's about the devastation left behind by nuclear armaments. And the schism between trying to live an ordinary life whilst having a nuclear Damocles sword waver over your head. That it became such a world wide hit makes it all the more ironic. I love it all the more for it.