Wormsinger/Wormfeeder Runes & related Keys - can you have more than one at a time?

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I've been holding on to a Key of Yuul for quite a while, mostly because I just have not gotten around to looking up a walk-through to point me in the direction of the chest. Meanwhile, I've noticed it seems that no Wormsinger/Wormfeeder Runes are spawning for me.
Are these Runes just extremely rare, or do I have to use the Key before a new Rune will drop?
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Where do I put Wormfeeder runes?
Once you land, turn around and look for a cave entrance. Inside and to the left will be a device that allows you to Insert Wormsinger Rune. The second location that you can use your Wormsinger Rune is also close to the Hull Breach spawn point.How do you use a Wormsinger Rune?
A Wormsinger Rune is a consumable found by killing Hive on the Dreadnaught during patrols or strikes. It can be used to activate a terminal located in a room beneath the Patrol spawn point. Once activated, a group of Acolyte and Knight majors will appear. Once they have been defeated, Blahgrish will be summoned.How do you get Wormsinger runes?
In order to obtain the Wormsinger Rune, you must kill Hive Wizards and Hive Knights while aboard the Dreadnaught, which is tricky since these specific enemies may be tough to find. We suggest going on patrol and spending time in the Court of Oryx in the hope of scoring a desired drop.Destiny: What to do with Wormsinger and Wormfeeder runes!
Sources: Stack Exchange - This article follows the attribution requirements of Stack Exchange and is licensed under CC BY-SA 3.0.
Images: Askar Abayev, Ylanite Koppens, Askar Abayev, Ketut Subiyanto