[abacadaba]

Correct Form: I didn't know that. He did it

[bccdee]

Once multiple sentences are on the table, it matters a lot less. The real significant line is between "zero periods; none needed" and "one redundant period at the end."

[adjkant]

OP here, I was very much referring to the last period, not periods in general.

[abacadaba]

I'm just glad I'm not the only one who's thought deeply about this :)