I've gone for a sequential part numbering system for my stuff. I've never really liked "intelligent" part numbering systems, possibly because I am not intelligent enough to remember what all the sub-numbers mean, and don't like having to try and classify parts and assemblies before I've even started work. PDM systems mean parts and assemblies are easy to find if the part descriptions are well chosen, and PDM doesn't have to be complicated. I use a spreadsheet for mine. Intermediate drawings (blank cutting with machining allowance, final machining, finishing etc) are done using part configurations. I appreciate this might not work so well for large organisations with lots of engineers and other staff needing to generate parts but it works well for me.