Are the World Runes a fixed set?

World Runes have been called 'League's equivalent of Weapons of Mass Destruction'(TB Skyen among others) as they contain an absolutely terrifying amount of power, we even see one used to level a city. This is a pretty simple idea, it's called a McGuffin and marvel has 6, But how many are there in League? I think that the cinematic 'Ryze: Call of Power' contains all the evidence we need in order to determine exactly how many world runes there are.

In the 'Ryze: Call of Power' short, we see the petricite (Magic dampening stone used and originating in Demacia) vault where Ryze keeps the world rune we see him get in the video. He places the World Rune inside a petricite column which I assume has some extra magic layered on top of petricite's natural magic dampening powers. in the intro to the scene however, we see Ryze walk towards the column where he places the World Rune and pass a number of other columns including some which are behind the others.

I counted the columns that the audience sees to Ryze's left as walks in the first scene as well as the final shot after he leaves using what is presumably realm warp and there were 6 columns. each of these is presumably mirrored on the right as the room is highly symmetrical. 6 x 2 = 12 plus one middle column where we can see Ryze place the red rune. we can see that this column has no mirror in the final shot after Ryze realm warps. This means that there are probably 13 World Runes in Ryze's Vault. Except that there aren't 13 World Runes in Ryze's Vault.

In the final shot of the cinematic, one of the 5 columns we can see has no World Rune in it. This clearly demonstrates that Ryze has created the pillar which will hold the rune before he even started the search for it as he was searching for the Red Rune he acquired during the Cinematic. This leads to the idea that Ryze might have made all the pillars before he got any world runes. If that were true then we while counting all the pillars cannot tell us how many World Runes Ryze has, it probably tells us how many there are in total.

There you have it, the evidence that there are 13 World Runes. That Ryze knows about, that being said he does have at least 4 knock off Infinity Stones, so I presume he's probably pretty close to omniscient. Also please like this post se we can maybe get some confirmation from RIOT or something.