Ms Access has some reserved words and I believe Date and Group are in that list.
see http://allenbrowne.com/AppIssueBadWord.html for the list.
You could change these fields to MyDate and MyGroup or your choice.
You could insert your daily /weekly possible append records to a Holding type table, say WorkTable.
Whatever the name of you ProductionTable is you should make a unique compound index on MyDate + MyGroup (since you said they are unique to each record).
If you import data from your weekly/daily additions file to your workTable, then a query like
Code:
Insert Into ProductionTable( each fleldname, next fieldname,....) From WorkTable
Where Worktable.MyDate & WorkTable.MyGroup Not In
(Select ProductionTable.MyDate & ProductionTable.MyGroup from ProductionTable)
Make sure you test this on a test version of your database, before running it against your "production copy".
Also all tables should have a primary key.
see http://www.techonthenet.com/sql/insert.php for Insert Into syntax