It's funny how themes come around in cycles.

This
will have been mentioned before (even just by me for example) - however...
Autonumbers aren't necessarily consecutive (as mentioned) nor are they unique or repositioning.
i.e. The values by an autonumber will generally be unique (because they're designed to increment). Only the
very common primary key on that field forces them to be unique.
Also a compact won't reposition an autonumber's seed back to the Max ID + 1 value.
That was the case for Jet versions prior to 4 and a bug in Jet 4 SP 5/6 saw that behaviour reappear briefly (it was about the time of Access 2002's release IIRC).
Similarly a bug around there saw values reused (which
is possible - although the PK will prevent it and raise an error) having seen the seed set almost randomly.
The higher value needn't have been achieved due to deleted rows. An inserted autonumber value of the higher value would have set the seed to that point.
The method suggested by DCB is appropriate to get back to where you want - you can also specify the seed value using ADOX.
As has also been said though, it's unusual for you to be in a position where you should care what the autonumber value is.
Cheers.