I know it

[Benjamin Barrett]

I've been wondering for some time if there's been a change in the
way questions are answered.

A: Did you know that there is a leap day in the year 2000?
B: Yes, I know it/that.

To me, only "that" is correct in this context, but I hear older
speakers use "it."

To me, "I know it" has a slightly different intonation and means "I
agree with you" or "I know what you're talking about."

Has anyone else noticed this?

Benjamin Barrett