Deb,
Another solution is to simply use the [Record ID#] to make a formula field to make a sequential number based off the Record ID# field.
ie "C-" & ToText([Record ID#])
It will not start with the Year number. You can import from excel and delete enough records to roll the record ID# ahead to say 30,000 and just count forward from there.
You may want to number based on the year, but there may really not be a good reason to do that, other than that is always how you used to do it.
So, I'm just offering up an alternative solution.