That's just based on something I've picked up from reading about and comparing photos of buttons with confirmed dates. I've studied Tice's authoritative book of military buttons quite a bit, too.
Generally, from what I've seen, a Waterbury button is likely pre- mid-1940s if it:
-still mentions "buttons" in some way
-has "company" in singular,
-uses a serif font
For example, "Waterbury Button Co." or "Waterbury B. Co." or "W.B.Co." in a serif font.
On the other hand, it's likely post mid-1940s if it:
- References Waterbury companies such as "Waterbury CO's"
- does not mention "button"
- has block lettering
As far a dating pre-civil war, civil war, and post civil war up to the mid 1940s, there's a lot more to it.