General :: Auto Generate Report Number When Required

We have a large split database with 3 users on a single site. We will soon be increasing this to 6 users across 2 sites.

One of the fields in the main table is "report number" where a line is given a unique number. Not every line is given this number, as it depends on the finished status of the product.

The numbers are currently hand written onto a sheet as they are used, which obviously avoids duplicates. This however will be near on impossible once the database is shared across 2 sites.

the format of the number is 00/0000 where the first two digits are the year, and the last four increase sequentially.

Is there a reasonably easy way to incorporate this into the database itself, where a number can be generated as required, as apposed to every time?