I might be completely off here, but I'm pretty sure it won't say "edited" if you make changes before somebody else has viewed your post. I've made some trip reports and added photo posts and then edited them later without them saying "edited".
Here's a trick I do if I'm changing something more than 30 seconds after I originally posted...
Type "edit:" and then say what you meant to say.
edit: Just testing my theory here. It probably won't say "edited" yet because nobody's looked at the page yet.