Symptoms
Is it possible to placeholders in enumerator class (Home>System>Settings>More Finance Settings>Enumerator Classes in PBA-E 5.5 or Home>Configuration Director>Document Numbering>Enumerator Classes in PBa-E 5.4), so it is possible to use year (and month) without manual action.
For example:
Enumerator INV/%y/0000 would translate to INV/14/0000. INV/%Y/%m/000 would translate to INV/2014/03/000.
Cause
Currently it is not possible to use any kind of placeholder in enumerator classes.
Resolution
Feature request to implement this functionality exists - PBA-55112 The only possible workaround for now is to manually change enumerator classes at the beginning of each month/year.