Modify Listbox Without Disturbing Previous Entries

How do you add or delete choices to a dropdown list without deleting all entries that were selected throughout the spreadsheet in the past, or having to change the validatons rules one by one?

I set up the list box choices (dropdown choices) by just naming the group of cells -- that is, by highlighting the group of cells, and typing a name into cell name field (in upper left corner of window); then using that name in data validation on the spreadsheet cell for the user.

- When I try to adjust the box, by adding entries and naming the revised group of cells with the old group name, it does not recognize the new group but the old group.

- If I delete old list and replace with new list, the previous entries disappear.

- When I try to name the new group a different name - it does work - but it involves changing the data validation on the user's spreadsheet, and skipping the ones that are already entered.

I wondered if there is a more efficient manageable way to maintain changes to the list items in a dropdown list box (one that is used for dependent lists) in Excel. I suspect it's easier in Access.