I have an existing list of unique identifiers that are text. They comprise of 4 characters and they all start with C. Example -- "C***". I also plan to add to this list but I need to create a VBA application that will automatically generate text to fill in the remaining 3 variables and also ensure that the new ID's do not conflict with the existing ID's.

I know this is tricky using text in lieu of an autonumber but I can't seem to find the answer. Any ideas would be appreciated.