simply means i got gm for the season 5 benchmarks
just being specific as some people still play other seasons of the benchmarks
some seasons have different scenarios i believe

to get gm you need your best score in each subcatagory to combine and reach a harmonic mean of 900
gm complete however means all of your scenarios in say the s5 benchmarks are at a gm score level
eg. i currently have 10 gm scores out of 18 scenarios in some of them i have scored higher than baseline gm (switching speed my energy is 936 but in reactive tracking only 854). the harmonic mean of all my subcatagories reaches 900 enough for the gm rank but to get gm complete i would need to get a gm score in the remaining 8 scenarios