You can set up a product version number rule to have a new version number defined based on the order of a predefined list.
Example: Your list is A, B, C, D, E. On first release, the product gets version number A. If version E is released, further version releases are blocked.

Standard procedure

1.	Go to Product engineering > Setup > Product version number rule.
2.	Click New.
3.	In the Name field, type a value.
4.	In the Number Rule field, select 'List'.
5.	You can define as many version numbers as required and define the sequence in which these are to be used.
	Click Add.
6.	In the Version field, type a value.
7.	Close the page.