Either gather the data via a stored proc, which would allow you to change the value

or

group by the position code and then you could use a formula (or a group of them)
in the group header:
shared booleanvar addend:=false;
shared numbervar ending:=0;
if count({table.positionCode}) > 1 then addend:=true;
addend;
""//hide the random true

in the detail section for the group code:
shared booleanvar addend;
shared numbervar ending;
if addend then (
ending := ending + 1;
{table.positionCode} + "/" + totext(ending,"",0);
)
else
{table.positionCode}

one of these should do it for you....

HTH