As an engine gets tired, it starts to burn more fuel, and more fuel means more ITT, EGT,ect. Also if your compressor starts to wear out, you start turning N1 faster to make up for loss of efficiency. Now if you start matching fuel flow on a miss matched airframe, you may end up worsening the condition of the engines. Now how exactly is the maintainers supose to fix a miss matched fuel flow? If you came and told me that your fuel flow was out, first thing I'd ask is what is your N1 and ITT.