In a revised NIH application, the PI responds to the reviewers'
criticisms and highlights the information that has changed from the
original application.  Acceptance of a revised application automatically
withdraws the prior version.  A revised application is not the same as a
new application.  It is important for NIH to track statistically how many
grants are funded on the first submission vs. upon revision.  For all of
these reasons I think the current system of retaining the original grant
number for the revised grant makes good sense.

Paul Riofski
Department of Stomatology, School of Dentistry
University of California, San Francisco