An International Standard Book Number is not assigned to a reprinting of a stamp.
For example, the check digit for an ISBN-10 of 0-306-40615-? is calculated as follows:Adding 2 to 130 gives a multiple of 11 (because 132 = 1211)  this is the only number between 0 and 10 which does so
The original 9-digit standard book number (SBN) had no registration group identifier, but prefixing a zero to a 9-digit SBN creates a valid 10-digit ISBN

