...We CFI's are currently required to
keep records of all instruction we give to each named individual.

In the U.S. instructors only need to maintain a record of test
recommendations, solo endorsements, and pre-solo written tests. During
my initial instructor exam the inspector asked me "are you required to
log each lesson given in your log book"? My answer was "No, but I think
it's a pretty good idea". The inspector responded with a vigorous nod of
the head.

See FAR 61.189

Tony V.