The value specified by CurrentRecord corresponds to the value shown in the record number box found in the lower-left corner of the form.
A primary key is, for example, an AutoNumber, a field data type that automatically stores a unique number for each record as it's added to a table.
Once a record is deleted, its primary key is gone also. A CurrentRecord number, however, might change.
If John Doe's CurrentRecord is 38, for example, if you delete records entered before his, the CurrentRecord will change; the primary key that was associated with the deleted records is gone forever.