You might want to rethink/rephrase a couple of these statements. ;)
Yep, this definitely works - Check the stats tab of the plugin and you will be able to see a history of when this plugin was first added to WordPress.
Not if the copycat is artificially boosting total number of downloads and bypasses you (no names, but yeah we know of a couple plugins doing this ;) - Check the number of downloads on the sidebar. The original plugin always gets more downloads than the copycats.
Same as above (no names:) ) - Check the number of ratings. The original plugin should have more votes.
Yep, this definitely works - Check the developer's site.
Those plugins are pretty easy to spot - total downloads doubled overnight ha ha ha and 5 times the normal number of votes/star ratings ha ha ha. Too funny.