Request for guidance from more intelligent people than me-Project Identification help

Our client just dropped a bomb on me and is getting rid of the only number that is associated with a project that is unique and carries through all projects. Until Friday, we had a total of 6 numbers that constituted the value tracking a project-I will not go into the whys.  But on Friday, I found out the are getting rid of the only one that is unique.

So of course, being 98% ready to go live, I have the rug yanked from under me while standing over the Grand Canyon.  I had to go back and revamp the app to add the new (#7) reference number and associated fields, and basically recreate the app.

My question to people in a similar boat, how can I make the app bulletproof for such a thing in the future?  I have currently created a field that is nothing more than the record ID# and calling it a project reference number so I can reference it from table to table and then hide that number but show the other numbers that are of value.  Does this make sense?  Is this a good method or is there something better that people can think of?

Thanks.