Hi ​@rachfig,

There are ways to achieve this scenario.
The easiest way is to have a lookup control lookup the list to see the last number and then add one. The issue here is that if two users submit at the same time, they will likely have looked up the same number; therefore, you will get duplicates.

The alternative is to use an SQL request action to lookup a database that keeps track of the next number. This would save development apart from creating a stored procedure.  Keeping a record of what numbers have already been given out would prevent duplicates.

Hi ​@rachfig 
Have you resolved your question? 

rachfig,

An alternative to Simon’s suggestions is to create a separate numbered reference list for each product. Every SP list has a sequential ID automatically created. You can prepopulate each product list for a given year and have a field indicating it’s been used, or you can create a new item each time and get the ID as the incrementing number. The latter would be better for cases when multiple requests might be occurring simultaneously. SharePoint will handle the timing and each one will get a unique ID.

Hope this helps,

Gerard