Even centuries later (1200s) the king Alfonso X the wise had to choose a main variety of Spanish among the ones that were used in the kingdom of Castilla y Leon

Even centuries later (1200s) the king Alfonso X the wise had to choose a main variety of Spanish among the ones that were used in the kingdom of Castilla y Leon. So I doubt any previous change in the language was a coincidence or fashion: the population that spoke old Spanish was so big and diverse that it’s nearly impossible for them to suffer the same events.