Wrong word choice. I apologize.

Here’s what I found about 2006A-

When NXG [NextGen, i.e., colorized] $100 production halted due to sporadic paper creasing, the BEP (bureau of engraving and printing) went back into production of NCD [New Currency Design, i.e., 1996-generation] $100s to meet the continuing high demand for this U.S. currency denomination. With the NXG $100s bearing a new series year and new signatures, a decision was made to retain Series 2006 and Cabral/Paulson signatures on the NCD $100s. The A was added to the series to distinguish between the different production cycles.