Hi,
It appears the numbers are 'lost' through buffering - To improve the performance, a set of numbers are buffered for the number range object on application servers. Where a server is shut down the numbers in the buffer are 'lost' and never issued. Where there are multiple servers, each server will also be given a set of numbers. These also may not be used.
If the numbers are to be assigned continuously, buffering the numbers can be deactivated using transaction SNRO with object QMEL_NR.
For performance reasons buffering is normally recommended. See note 62077 which contains more information on this concept.
-Paul
