document updated 11 years ago, on Feb 29, 2012
It is possible to lose track of some versions. In other cases, the versions just seem to disappear, but really are just temporarily out of view.
Ways to view these:
git log --walk-reflogs
gitk --all $( git log --walk-reflogs --format='%H' )
gitk --all $( git rev-list --all --walk-reflogs )
git fsck --unreachable
That's not all... there are several other instances where you can revive seemingly lost versions, to the point that some people suggest that git never lets you truly lose anything.