When I use the "reserve number" function for a batch of numbers to use in an ipart table I can easily paste those numbers in to the table and it works fine. e.g. P-01-0001 through to P-01-0008.
I may then add an extra instance onto the ipart table (P-01-0009) without reserving it first.
At a later date I may want to add other instances, (which should start at P-01-0010). However, when I go to "reserve number" it gives me P-01-0009 which has already been taken.
The "reserve number" function would be better if it looked at Vault to find which numbers are already in use.