Only the Gray squirrels bury the nuts they find and they do find most of the nuts they've buried but they don't remember where all their nuts are buried and sometimes don't find them all.
Gray squirrels typically only find around 26% of the nuts they've buried and the rest of the nuts that they leave in the ground then eventually germinate into trees.
The red squirrels only horde their nuts above ground so they're much easier to find.