If you return to the U.S. prior to September 2013 you will not need a new visa stamp at all -- you travel with a current passport, old visa stamp and new H-1B approval plus curernt letter from Employer B that you have a job to return to.
Visa stamping is a separate issue and discretionary on the part of the consulate whether they will consider you for visa stamping or not. Generally when you already have a stamp many third countries will process your case if their workload is not too high.
Lynne R. Feldman, Attorney at Law
Concentrating in Immigration and Nationality Law
2221 Camino Del Rio South, Suite 201
San Diego, CA 92108
phone: (619) 299-9600, facsimile: (619) 923-3277
Formerly Adjunct Professor -- Immigration law
University of Illinois College of Law
No one can guarantee that a visa will be issued.
J Charles Ferrari Eng & Nishimura 213.622.2255 The statement above is general in nature and does not constitute legal advice, as not all the facts are known. You should retain an attorney to review all the facts specific to your case in order to receive advise specific to your case. The statement above does not create an attorney/client relationship. Answers on Avvo can only be general ones, as specific answers would require knowledge of all the facts. As such, they may or may not apply to the question.