Is it also fair to say "use your best judgement" on claiming partial events? The times on the website appear to be auto-populated based on when the leader adds them to the event. For example, looking at Fog's PvE event from last night, I see various objectives spanning 6-ish to 8-ish pm, and I presume that he was adding them as we went. Not every event leader seems to do it this way, however, as several of the WvW events have dozens of objectives logged in the space of about 10 minutes - either they're super awesome fast (which I won't rule out), or they're logging everything at the end.
Now, it hardly seems fair to require event leaders to log their objectives in real-time. Sometimes things just move too fast for that to be feasible, especially in situations like WvW. A better answer, I would think, is to say "use your best judgement".
For example, I did WvW one night, and was there for 2 of the scheduled 3 hours. By morning, when I went to claim the event, I wasn't sure which objectives we took how many times, and I'm not really sure what denotes a "Defend" objective. Also, I don't really know the names of everything in WvW yet, I pretty much stick with the zerg, do what I'm told, and make red things die. I wound up claiming 2/3 (rounded down) of the objectives, relying on memory and judgement to select which to claim.
Is this a reasonable thing to do?
Yes, it's nit-picky of me to even bring this up, but it's there, and it'll come up eventually anyway.