Official Document Numbering 
Use
In Italy, the numbering of invoices and credit memos that have to be reported on the VAT register has to start at the beginning of the calendar year, so the first number in the range is assigned on January 1st each year. For this purpose, it is required that document number ranges are linked to the calendar year, rather than the fiscal year. Furthermore, the official document number (ODN) assigned to such documents has to be consecutive without gaps. The SAP system provides functions to number documents according to these requirements.
Prerequisites
You have to make the settings described in Customizing for Cross-Application Components by choosing General Application Functions® Cross-Application Document Numbering ® Italy.
The menu path in this documentation refers to mySAP ERP 2005 and higher. If you cannot access the Customizing activities in lower releases using the menu path listed above, you can make the relevant assignments in transaction SM30, as follows:
1. Define document classes in view V_DOCCLS.
2. Assign document classes to document types in view V_T003_B_I.
3. Maintain number ranges in transaction FGSODN_IT2.
4. Assign number ranges to document classes in view V_OFFNUM_IT.
Features
Depending on the settings you make in Customizing, the system enables you to maintain year-dependent number ranges for the official document number for a company code. It then automatically generates the official document number within the year-dependent number range on SD and MM documents when you post them. It also runs a chronological check on the document numbers to ensure they are consecutive with no gaps.