They don't always match - but they mostly do. When they match, it's a quite likely confirmation that they belong together. If they don't match, it could be that it was made like that, or that it's an assembly of sorts afterwards.
I don't think anyone knows 100% what the number codes mean, but the most popular theory is they are MM=DD date codes. This is on the basis that nobody has seen the first number higher than 12, or the second higher than 31.
I have a 100% original 1978 Springy with body and neck codes 12=10 and 12=9. It seems quite plausible they were manufactured one day apart.