multiple auto numbering systems

This is how I have done something similar before. I would have a separate table for the Types and then have a parent child relationship between Types and the Projects table. Types is the parent and Projects is the Child. Then have a summary field on that relationship for # of Projects-A and make sure this is a count of the Projects where the related type field = "A". Similarly for B, C and so forth. Then pull these fields to the Projects table as look fields from the Types table. Then write a formula field for Project Number such that, if it is A, then it would be 50000 + that max value for A (which you brought as lookup) and take the Right most 5 characters. If it is B, 60000 + that max for B and so on. Hope this helps,