for all (one) knows
Said when one is uncertain or has limited details about something. I haven't talked to Marie in weeks, so, for all I know, she's not even coming to the dinner party tonight.
for all someone knows
COMMON You use for all someone knows to say that person does not know the facts of a situation. For all we know, he may even not be in this country. She's had a miserable time staying faithful to someone who for all she knows might not be coming back.
for all someone knows
used to express the limited scope or extent of someone's information.