unrecollected
unrecallable
unforeshadowed
unexacted
on the tip of one's tongue
nonrecollection
unrecounted
ungraspable
unguessed
unremembered
unreminded
nondetermined
unreconnoitred
block
blank out
forget
draw a blank
unsurmising
oblivious
nonbriefed
unbriefed
nonanecdotal
nonexplanatory
unthought
unrecalled
unremembering
unpinpointed
unforeknowable
unfactual
undescried
unrememberable
unenvisaged
unforeheard
nonchronological
ungleaned
unbeknown
unchronological
nondiscerning
unrectified
unnoted
undiscerning
nonrectified
unmemorized
untraced
unharked
unexperienced
nonfamiliar
unchronologically
nonrecordable
unrevitalized