so you are sorting ascending on the field and since it sorts in a particluar sequence you expect that if you use a a < or > it would return values comaprible to the sort, correct?
I do not know what the rules are in terms of using < and > on strings but I they never match my expecations using a alpha sort.
If you look in Crystal Help under the StrCmp function you will see examples of this.
On your current report stick a formula field in as
strcmp({myfile.mycode},next({myfile.mycode}))
You will get avalues of -1 (the row is < the next row), 0 (the row = the next row) and 1 (the row is > the next row). YOu will see it doe snot follow the same logic as alpha sorting.