How Are Series Years On Currency Chosen.

The series year typically changes with a design change or a signature change. When there is a new presidential administration with changes in the Secretary of the Treasury and/or United States Treasurer, the series will change. A letter, "A" was added to the 2017 series with a change in the ink or paper used. The BEP has been somewhat secretive about the latest changes. There are however, exceptions to this. Series 2006 $5 notes had a major design change without a series change. Both of these are series 2006 $5 notes.

Going back to the first small size notes in 1928, there has never been a consistent and reliable standard for the change in Series dates and letter appendages.

I think 1935 $1 SC's has the highest suffix (H).

Any idea when the first banknotes with Mrs Yellen's signature will be printed and then released?
What has been the usual time frame for a series change after a new Secretary of the Treasury takes office?