actually i believe you could find out who saw them with 2 triggers:
nvm, 2 triggers and a script...
trigger 1:
west detected by east
on activation:found=true;found_units=thislist; and anything else you want
trigger 2:
covering whole map
east present (probably repeatedly, depends on the situation)
condition:this and found
on activation: thislist exec "whoknows.sqs"
_found = found_units
_east_units = this
_finders = []
{?_x knowsabout ({_x} foreach _found) > 2:_finders = _finders + _x} foreach _east_units
hint format ["%1 have found the west units",_finders]
i believe 2 is the correct knowsabout value (more or less) for whether a unit has been identified. this isn't garunteed, especially since that coupling of foreach might be a bit touchy....