On wednesday, during our weekly warzone get together with the customs crew Inhuman and I had a lengthy disussion about Halo: Reach and how 343i has shaped it into the canon. Inhuman mentioned multiple times that most of the events taking place in the first half of the game are canonically nothing more than ONI propoganda. That they created a secret stealth invasion to make it seem that the covenant had to use covert ops and stealth to take on the UNSC version of the Pentagon, Reach. This fleet also consistes of a CSO class supercarrier, a ship that Inhuman also stated isn't a real thing and is also ONI propaganda. So, as I do, I harnassed my inner Ahab and went after my white whale, the elusive Fleet of Valiant Prudence and its flagship the Long Night of Solace.

First here is the link to the stream where we had the conversation
1:42:15-1:50:50
Aslo, thanks Vagueness for streaming all of our conversations, it makes things a ton easier.

A quick and very brief correction on my part, I was confusing the CSO supercarrier with the CAS assualtcarrier. The ship Regret took to New Mombasa in Halo 2 is a CAS assualtcarrier not a CSO super carrier, which led to our confusion when we began to talk about Halo: Fleet Battles because both the CSO and the CAS have been made as models, so I mistook the CAS as a CSO. Also, look at the craziness that is the CSO model

That litte ship in the bottom left is a CAS in the same scale.

So its easy to say that the CSO is on a whole other level to most covenant ships and the only on screen mention of this massive ship is as the flagship of the Fleet of Valiant Prudence which was apparently an artifact retrieval fleet sent ahead of the main Fleet of Particular Justice to Reach. Based on this information it is quite plausible that the Fleet of Valiant Prudence is completely made up from an in universe perspective.
This quote is pulled directly from the Halopedia article about the CAS
"A further testament to this vessel's survivability is that it was selected by the Covenant alongside the much larger CSO-class supercarrier to serve as the Hierarchs' personal flagships when they were not aboard the also heavily shielded High Charity."
Perhaps this means that the prophets would exclusively fly CSO's as their flagship but due to Regret's small fleet sent to Earth he only used the smaller CAS instead. Either way, the fact that the CSO looks like a blown up CAS and that our only in universe appearence of this massive ship is in Reach, its quite possible that the CSO doesn't exist and is purely a result of ONI performing damage control after the Fall of Reach.