I think you have to read this one generously. The claim isn't about how COBOL works, except incidentally. It's more along the following lines:
COBOL doesn't have a default date/time type
As such implementation decisions are left to the implementor
The implementors* of the SS system chose 1875 as the epoch date for reasons
*I made a lot of money in 1999. The original implementors of SS probably used something else ("it'll be rewritten before this is a problem" was essentially the whole raison de etre of Y2K). The 1875 thing, if it's a thing, was probably the result of Y2K work. But I have no direct knowledge of these matters.
COBOL doesn't have a default date/time type
As such implementation decisions are left to the implementor
The implementors* of the SS system chose 1875 as the epoch date for reasons
*I made a lot of money in 1999. The original implementors of SS probably used something else ("it'll be rewritten before this is a problem" was essentially the whole raison de etre of Y2K). The 1875 thing, if it's a thing, was probably the result of Y2K work. But I have no direct knowledge of these matters.