Let's not confuse the difference between gaps in the sequence of AutoNumbers, which is a completely normal byproduct of how they are generated (and occasionally discarded without being used), and the actual subsequent deletion of records that were previously saved and visible.
The fact that you see gaps doesn't prove records were deleted, in other words.
If you can demonstrate by other means that records have been deleted, the gap in the sequence might be a useful way to isolate the relative time when they were entered (assuming you have date/time fields in records you can use to triangulate on when the record should have been entered).
Once again, please confirm that the records were physically present in a table, not just displayed in a form, prior to being deleted. I am very suspicious, in fact, that the records seem to be displayed in a continuous view form from which they disappear, and I would really be grateful for confirmation that you can, in fact, see the table with those records in it at some point.
If so, you can put a time frame around the disappearance of the records. It may well be that, if there is some delay involved, processes other than what you see only in that form have been invoked elsewhere.