Ah, you've all beaten me to it, and after I spent last night working through the W & B data for all the 172 marks I had data for (M, N, P, R, & S)
Anyway since I've done it you're going to get it
I initially thought KCDW might have been looking at the aft CG limit for the Utility category, rather than the normal category, but these are a bit further back (~41")
The CG envelope on the marks of 172 I looked at seem to be pretty similar, albeit with different maximum AUWs. Forward CG limit is 35" upto about 1950lbs, then a straight line to either 38.5 or 39.5 (depending on mark letter) at MAUW, with the max reaward at 47.3"
According to my calculations you'd have been able to get everyone + 20lbs baggage into all of the marks, but with differing fuel loads to remain within max weight. The best was the 172P, with 32US gallons, and the worst was the 172 R with only 14 US gallons
I reckon you'd have to try pretty had to load the aircraft beyond its max rearward CofG position, but its very easy to load it beyond MAUW
NB Reims made at least 3 marks of 172 (M, N, & P are the ones I know about), all with different MAUW.
Just for comparison, I also did the calcs for a 182 RG, where you'd have got everybody in, with full fuel, and 20lbs of bags
Brooklands