We've recently had some confusion about how DOI deposit fees are calculated from deposits. The process is straightforward for most deposits: a DOI is determined to be either back year or current year deposit based on the date included in the <publication_date> element.
We allow deposit of both online and print publication dates. When a DOI is deposited with both a print and online publication date the print date is used to determine the deposit fee. When depositing journals or other series or set types, be aware that each individual item is considered separately, regardless of the publication year included at the journal volume or issue level. For example, a deposit including both a print publication date of 1990 and an online date of 2010 at the issue level and only an online publication date of 2010 at the article level will be considered a current year deposit. If the print date of 1990 is included at the article level, the back year fee will be charged.
In summary: If you include both online and print publication dates in your deposits and want to avoid being charged the current year fee for back year deposits, be sure to include the print date at the article, chapter, or component level.