What is the answer to this economics question?

One question on an assignment I'm doing for office administration :

"The customer has been given a numeric code (116) as a reference. What advantage does numbering have over alphabetic referencing in terms of ensuring accuracy?"

This is in relation to a CUSTOMER NUMBER on a CREDIT NOTE giving credit for an item listed on a sales INVOICE.

Half the answer I originally gave was marked wrong and I was given it back to redo. The first point I made was correct ("numbers are more easily able to be allocated to customers and provide more individuality, which means more accuracy")

I then tried to back the point up by rambling on about an alphabetic labelling being too lengthy whereas numbers are shorter, which was the wrong part - I ran out of ideas while writing it).

Any ideas what a good answer to this question might be?