In the 19th century (before 1850) one pair probably met and maybe quite close to the published coordinates. The other pair could have met in the 20th century (after 1970), but I don't know if they ever did. If they did meet in the 20th century, then I like to imagine them meeting at places close to one or more of the following locations. Close means within 1 km.
A S 37 47.900, E 144 54.000
B S 38 09.000, E 144 20.800
C S 37 49.600, E 144 59.000
D S 37 48.000, E 144 58.700
E S 37 46.000, E 144 57.700
Notes:
1) Each member of this "set" of locations is close to a place that I know that members of one pair each "visited" at least once, albeit at different times in the 20th century.
2) Your goal is to find two values for each of the above letters (the higher value at A is denoted A and the lower value is denoted a; ditto for the other locations)
3) As GC21QMN is to GC1ZEZG, so GC2J5WZ is to GC2HMAR (v. important)
The cache is at
N 51 [501*(D-d) + E*d*c*A - 22*(a+1)]/1000
W 000 [479*(C*E*d) - C*D*c + 10*(d+e+b+3)]/1000