Need some help rounding out a Spartan OC

So, at the moment I’m trying to create a Spartan OC to feel a little more immersed when playing multiplayer across all Halo games. I want to keep his information reasonably understandable but also add some specifics to really ground him into the universe. Right now, I’m having trouble, specifically with affiliations. I’ve used references from Halopedia to write most of what I have on him, but I’m a little stumped.

To keep things simple: He’s a Spartan-III who is part of the UNSC navy and did a host of reconnaissance and assassination missions before eventually leaving to fight for his homeworld of Reach during it’s fall. He ended up surviving the ordeal, and is still alive as of the current Halo timeline, meaning he’d be present during the events of Infinite.

With that being said, everything else is pretty much solid. But while looking into the main group of Spartan-IIIs from Noble team, I noticed that most, if not all of them, had left the UNSC Navy to join the UNSC army. I did some research and found out some differences between the two branches, but I’m confused as to how to lay it all out in a bio template For reference, here’s what I got so far:

Affiliations: UNSC Navy (formerly), Naval Special Weapons, SPARTAN-III program, UNSC Army (formerly), Spartan Operations

My main concern is making it so that each branch doesn’t conflict with one another. I want to make sure his affiliations are displayed in a way that isn’t messy. For example, as far as I know, a soldier cannot be housed within the navy, while also being in the army. The same applies to my list of affiliations. Since he fought for Reach with a team during it’s fall, I’d assume he would have had to leave the navy to take part in it’s defense via the army. So, if he survived, and didn’t retire, would he need to leave the army in order to do Spartan ops? Or would he be able to do both? I know this is all super nit-picky and probably hella cringe, but I’m a writer and I like to make established characters for any media I enjoy or create. So if any of you veteran Halo fans could help a guy out in making sure his character isn’t a Mary Sue, I’d GREATLY appreciate it.

Finally, since I’m new to posting forums on Halo Waypoint, please let me know if this type of post is redundant, as I’ve seen some admins tell other users who make certain topics to post on an already pre-established one. If any of you need more details on my Spartan, his backstory can be read on my profile’s bio. Otherwise, thank you for reading and I hope to hear from you all soon!