X and Light Armor Capsules.

With the lack of info regarding X and Light Armor Capsules, I'd like to introduce another plausible theory: that the Armor having always been contained within X. Merely needing unlocked.

With that said, I shall start the Theory.

During X's design and completion, Light had a revelation: that his life is coming to it's end, and his plans for X haven't been completed yet. Once X was fully constructed, Light built a Capsule in order to maintain and finish X's mind. For his realization. Now, according to the Day of Sigma OVA, Light and X have conversed, this applies with the theory. Light was able to finish X's mind to a degree, but was unable to complete it. This is where the initial Capsule comes from.

However, the Capsule and Light had another plan in motion. A means to control X's power development. Since Light feared what X could become had he opted to become destructive.

So Light had encrypted data within X. To limit his power. This is the foundation of X's potential. Light having encrypted X with data locks in order to maintain X at a level of stability. But after his realization, and becoming a Hunter, he has faced enemies that need more power to defeat. To keep true to his promise to Light: Fighting for Justice. And when these times happen, X can stumble across a Capsule from Light. Be it the very same or different Capsules, I won't evaluate.

But upon locating these Capsules, X is reminded of Light. His promise and the 'gift' granted by Light for X to enforce. This is Light's link to X's data pool. Once X has established a connection with the Capsule, the data transfer unlocks a certain degree of ability within specific areas of X's body. This enhances his ability, and increases his potential.

However, the data unlocking is not permanent. The data seems to only be fully manifest within a temporary Memory drive within X. Which is why he doesn't keep his Armor intact. Some abilities remain, as in X's Dash function. It remains, because X has a constant use for it. his buster changes the first few interactions as well. Since he is always fighting. So such abilities remain due to constant use. This may be reasonable to interpreting them being ported to X's main memory.

Boss DNA based weapons fall under the temporary Memory as well.

After the Armor retracts back within X, the threat has been subsided. And the Capsule(s) hide once again for the next time needed.

X5 and X6 are different cases for the Memory. Since Alia copies the data for the Armor and reworks the code to have it remain longer. Which is why X keeps the Fourth (Force) and Falcon Armors. That is thanks to Alia.

And as for the Program Data used in X5 and X6. For Virus Security Protocol, the Armor data is obtained from X. Reworked into a recognizable coded program and is reinstalled into X. So Alia can assemble the Coded program and cause the Armor to manifest. But the Armor will always retract. Since X only needs it when forced by an enemy.

So, in short, X has the armor. Light Capsules is key to get to the Armor. The Armor isn't permanent and varies due to nature and severity of the conflict.