statikk shiv has shiv lightning and rapid fire cannon has firecannon. different names mean different uniques. you could even have kircheis shard there too. thing is that the stacks dont stack faster and when one of them goes off they all go off. so they actually do stack. just not on building stacks.
You probably shouldn't be naming people without their permission, even if this isn't quite name and shame.
As for your point, it's only partially correct. When you have both shiv and rfc (and potentially a shard too), you only get the extra damage from whatever the most effective one is in the given situation. Upon release they all stacked, but riot changed it since it was a bit too bursty, particularly for items built on adcs who tend to be more about sustained damage.
