I ran into an interesting scenario yesterday. I checked a simple assembly into Vault Professional 2015, assigned Items with the brand-spanking new item assignment process and all was great until I noticed the bold yellow highlighting in my Item BOM, focused on the Position Number column. “Huh?, I thought this was supposed to be automatic?”
After some tweating back and forth with Scott and Chris Benner I had one of those “Ah-ha!” moments. In Inventor, for the assembly, I enabled the Structured tab within the Bill of Materials. I updated the items, and BOOM! there were the position numbers.