I was recently working for a client who wanted to make use of the Automated numbering in SharePoint Lists. He wanted to create new items which will auto have reference numbers.
To do this I adviced him to make use of the ID column in SharePoint. So I created a calculated column so I can make use of the ID column in a calculation.
I created a new column "Reference Number" made it Calculated and in the calculation added =[ID] by doing this. It always uses the ID data as the reference number.