Firstly, I did spot one mistake I'd made in the Click event procedure of the search button in the subform. To turn off any curent filters the code should have been:
' turn off filter
Me.FilterOn = False
Me.Parent.FilterOn = False
Also I found an error in the Click event of the search button on the parent form. It should read:
' inform user if no matching records found
MsgBox "Sorry, no such record '" & Me.HeaderSN & "' was found.", _
vbOKOnly + vbInformation
The DataEntry property must be set to False (No) for the form to return previously entered records, and yes, you will be able to edit them. To open the form at an empty new record put the following code in its Load event procedure:
As regards the LinkMasterFields and LinkChildFields properties, inserting multiple values from columns in a referenced table is only valid if they are part of the referenced table's composite primary key, and therefore a part of a composite foreign key in the referencing table. Otherwise they introduce redundancy and the risk of update anomalies. The values can always be returned by joining the tables in a query, or by means of unbound controls in a form.
As far as other design faults go, I'll just mention two obvious ones. Two of your tables, Header Data and Surrogate Data, have no primary key designated. Every table must have a primary key, which can be one column of distinct values, or a set of columns whose values in combination are distinct.
None of the relationships in the database have referential integrity enforced. An unenforced relationship serves no purpose whatsoever, and leaves the database wide open to invalid data being inserted.
I would strongly advise that you spend some time studying the principles of the database relational model, particularly the process of normalization. You might like to take a look at DatabaseBasics.zip and Normalizatio.zip in my public databases folder at:
https://onedrive.live.com/?cid=44CC60D7FEA42912&id=44CC60D7FEA42912!169
If you have trouble downloading a specific file, clicking on the 'Download' button at the top of the page while no files are selected should download a zip file of all files in the folder, from which you should then be able to unpack the relevant file.