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So, the facts I've found:
- in contact sport a layer is regularly exposed to strikes to the head/body. This increases chance of c/TBI.
-The articles in that search are more often than not, with players wearing helmets ect which would require a greater force to overcome such protection.
-There are cases of 120g with no concussion.
-There are cases with 20g resulting in concussion.
-Direct force to head is not always the case, rotational and lineal forces ect are very hard to measure and research is being done but results are not concluded.
-there are cases of regular 2g force, from spinning in skating, leading to persistent concussion symptoms
-Newton's 3rd law should always be considered, but is often hard to factor in injury incidences.
-it is possible a slap will cause 100's of g force, briefly to a local area, with no damage
-sustained low g force can cause much damage/death, specially if it is of the same frequency of an organ.
-underlying cardiovascular issues decrease g force tolerance
-g force tolerance can be increased by training or countering if blow is seen coming

In conclusion, it is incorrect to say that a 70-90 g force is required for concussion. At best this is a generalisation. There are simply too many variables. I spent 15 minutes researching.