Printing Year Question

The A under the date has nothing to do with the SN.It has to do with a Signature change.
John1

To complete the answer

The series (2006) changes when the Secretary of the Treasury changes
The suffix (A) changes when the Treasurer of the Unites States changes

Quoting treasury.gov:

Jacob J. Lew
Secretary of the Treasury

Jack Lew was confirmed by the United States Senate on February 27, 2013, to serve as the 76th Secretary of the Treasury. Secretary Lew previously served as White House Chief of Staff. Prior to that role, Lew was the Director of the Office of Management and Budget (OMB), a position he also held in President Clinton's Cabinet from 1998 to 2001. Before returning to OMB in 2010, Lew first joined the Obama Administration as Deputy Secretary of State for Management and Resources.



Rosie Rios serves as the 43rd Treasurer of the United States. She has direct oversight over the U.S. Mint, the Bureau of Engraving and Printing and FortKnox and is a key liaison with the Federal Reserve. In addition, the Treasurer serves as a senior advisor to the Secretary in the areas of community development and public engagement. She is especially passionate about supporting Women in Finance and issues of Main Street in the economic recovery.

Prior to her confirmation as Treasurer, Rios worked at MacFarlane Partners, where she was Managing Director of Investments. Working with MacFarlane Partners' development and global capital partners, Rios played a central role in facilitating equity transactions for large mixed-use development projects in major urban areas. In November of 2008, Rios took a leave of absence from MacFarlane Partners to serve on the Treasury/Federal Reserve Transition Team and is a graduate of Harvard University.


http://www.coincommunity.com/us_1_dollar_notes/

So were Mr. Lew to resign the next bills would be series 2014. But were Ms. Rios to resign the next bills would be series 2013A.

There is also the recent precedent of the $100 bills where the original printing (2009) is in storage to be inspected for the printing issues, while the reprint (2009A) has been released. And thus denco7's statement is partly correct.

It gets complex because they don't always print every denomination - see http://www.uspapermoney.info/serials/

True, with two recent exceptions.

They stopped printing Series 2006 hundred dollar bills when they started printing the Series 2009 (there may have been overlap by a month or two; the BEP usually uses plates until they need retiring). But with the production problems on the 2009 hundreds, they re-started 2006, but labeled them as Series 2006A while printing of the 2009 hundreds was suspended to work some bugs out.

Once they got that fixed, when they resumed the hundreds, they were dated 2009A.

In both of these instances, the signatures from 2006/2006A did not change, and neither did they for 2009/2009A.

It will be interesting if we have a change in the Treasurer before her term expires....the hundreds will go to 2009B, but will the lower notes also make that jump? Or will they be 2009A?