for all someone knows

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.
See also: all, know
Farlex Dictionary of Idioms.

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.
See also: all, know, someone
Collins COBUILD Idioms Dictionary, 3rd ed.

for all someone knows

used to express the limited scope or extent of someone's information.
See also: all, know, someone
Farlex Partner Idioms Dictionary
See also:
  • for all (one) knows
  • for all I know
  • for all I, you, etc. know
  • happen to
  • haul (something) from (something or some place)
  • scratch (one's) head
  • scratch one's head
  • scratch your head
  • Are you writing a book?
  • dialogue with