Someone correct me if I'm wrong... but nowadays the "standard" size for the 1A is 650, with the option of 664. It's the older 1As from the 60s forward that had 664 as standard. I don't know when they switched to the smaller scale, though.
Not a miscalculation: it was a deliberate effort to make the guitar's sound bigger and louder. Some people, notably those with larger hands, prefer the 664. One thing I did love about it was the wider string spacing for the right hand. But the 1A (older ones, I mean) is not known as one of the more easy-to-play guitars; my old teacher said mine was like "playing a 2x4". But it is what it is, and is beloved for that unique, characteristic, beautiful sound.
(For what it's worth, I play a 640 guitar now...!)
2015 Connor spruce/Indian rosewood
1978 Ramirez 1a cedar