The answer is right, but not complete in my humble opinion.

If you want to know, if somebody accepted and attached/rezzed this object, so you'll have to add a script into the object itself.

You use the function "on_rez(){}" or "state_entry(){ }" and let the object inform you, that llDetected_Key(0) has rezzed the object. Or you can send an email to the server, which sent the object to specified residents with some informations WHAT was rezzed/attached and WHO has rezzed/attached.

Then a serverscript can analyse and compare the list of receivers with the list of "openers".