Go ahead and ask him for the cel number.  One of 
two things can happen.  Either he is slightly 
worried that the cel's might match, people do 
make forgeries, and some people make very good 
one's, and would want to know if something is 
amiss, or he is trying to forge stuff.  The 
second is very unlikely, and because of that i 
don't believe he will have any problem with 
letting you know the production number.