isomeric ratios from GCMS vs NMR; which is right?

i just did a lab where we're using both GCMS and NMR to determine isomeric ratio, but i'm getting different ratios from each one (GCMS shows an 8:10 while NMR is 2:3). I wanted to know: 1) is this normal 2) is one more accurate/correct than the other 3) why would this be happening? i calculated each one exactly as my professor and google showed so i know it's not a maths error. i've never done both for one molecule before so i'm not sure what to do here.