The locations might vary depending on difficulty setting. Maybe the locations listed in the manual are for easy or normal. I'll take a quick peak at the DLL file.
Edit: They do. The locations are fixed for two difficulty settings, and random for the third. They are fixed in sets of 3 though, so once you find one, you can use that to find the others. It looks like on hard, the 3 locations could be at either of the 3 easy locations, the 3 normal locations, or at 3 new hard locations.
Provided I haven't made an errors (reading the hex values placed into the right registers, converting hex to decimal, and adding the proper offsets), the possible locations are:
Easy (or Hard)
-----------------
(31, 2)
(90, 9)
(116, 52)
Normal (or Hard)
-------------------
(7, 7)
(90, 30)
(114, 35)
Hard (only)
-------------
(41, 11)
(67, 58)
(119, 24)
Remember that on hard it selects one of the sets with a 1/3 probability.
Curiously enough, I didn't find your second coordinate anywhere in my list.