I presume the original designer never expected to ever reach Z, or didn't care. Or perhaps by the time one gets to Z you have archived/deleted A. The back story I found out last night was that this was never a SQL Server database to begin with. It started its life as a proprietary format written in VB3, before going through a few iterations of other databases (Filemaker was mentioned) before finally ending up living on an old SQL 6.5 Instance. Which later got detached and re-attached to SQL7 and we received it after it was converted to 2005. So it's been around.

And, we are totally fixing it when it gets absorbed into our normal CRM over the next few months. It was more a thought experiment than anything else.