Yes...
You have missed something.

try the following code to see the result:

?OCCURS(SPACE(2),strtran(space(1)+'a'+space(2)+'b'+space(3)+'c'+space(4)+'d',space(2),space(1)))

Strtran works only from left-to-right and replaces the first occurance of overlaping strings
so

?len(strtran(space(3),space(2),space(1)))

will say '2' which is correct:
two spaces replaced by one + one remaining space.

To clear all dublicates of spaces run strtran in a cycle, till the length of the string is not changed from that before the strtran

Best wishesh