The Vermont stamp doesn't add to its value.
Please see the related question for more information.
About a dollar.
Yes. They were only issued as series 1988A, because a new US Treasurer had been appointed before the bills were printed.
Series 1981 $100 bills have the signatures of Treasury Secretary Donald Regan and US Treasurer Angela Buchanan. Series 1981 A bills were issued when Buchanan was replaced by Katherine Ortega.
Dorothy Andrews Elston Kabis was the 33rd treasurer of the US
The date on a bill is not the year it was printed, it's the so-called "series" under which the bill was issued. Normally when a new Secretary of the Treasury is appointed, a new series is started. When a new Treasurer is appointed, a small letter is appended to the date. Because Henry Paulson was appointed as Treasury Secretary in 2006, bills bearing his signature are thus all dated Series 2006. If a new Treasurer is appointed before the end of the year those bills will read "2006 A". When a new Secretary is named in 2009, those bills will be Series 2009.
The television series Newhart is set in the American state of Vermont. The series is about an american couple that own and operate a Inn in a rural town in Vermont.
The Tunbridge Soil series.
Probably never. Modern practice is to add a series letter only when a new Treasurer is appointed, and to start a new series year whenever a new Secretary of the Treasury is appointed.The 2006 series started when Henry Paulson became Secretary of the Treasury but he left office when the Republicans were defeated in 2008. Once the current supply of bills runs out a new 2009 or 2010 series with Tim Geithner's signature will be printed.
Newhart
All dollar bills have signatures printed on them; one is the Secretary of the Treasury, and the other is the U.S. Treasurer. An uncirculated series 1974 might sell for a few dollars, but it's not especially valuable.
a lot
There is no specific date on modern U.S. currency. On current bills, the series date changes when a new design is issued or a new Treasury Secretary is appointed. A letter is added after the date when a new Treasurer takes office. However the same date and letter may be used for months or even years.