Batch numbers need not be sequential and need not represent a full month. They need only be unique within a calendar year. Each producer or importer of renewable fuel can define a batch in whatever way it chooses, so long as each batch represents less than 100 million gallon-RINs and no more than one calendar month's production.
See regulation Sections 80.1125(e) and 80.1126(c). Examples of permissible batch numbering schemes include individual tankfulls, calendar day production, weekly production, and volume sold to each customer each month.
Question and Answer was originally posted at: Questions and Answers on the Renewable Fuel Standard Program (PDF) (55 pp, 221 K, EPA420-F-07-041a, August 2007, About PDF)