Yes and no. I'd say OS theory is also helpful when writing programs that run on an OS.
In the same way network theory is helpful when writing programs that communicate on a network.
I find I've retained a lot of my CS theory, but in a "quiet" way. [1] It only really surfaces when I'm talking about things with colleagues, and I take some information for granted, but ultimately work out they don't have the same understanding.
I do a fair bit of database work, and all that normalisation, foreign keys, relationships knowledge is "just there". On the other hand I only very occasionally have cause to do graphics work, so I remember the very basics, but not much else.
I also remember we did things, which I haven't used for 30 years, but which "holds no fear". I recently had cause to consider writing some code in assembly, and it may or may not happen, but either way I have no "fear" of what it entails, its "just assembly code."
So to the OP I say, your CS degree isn't about facts. It's about an understanding of how things fit together, and in your career you'll use that knowledge in ways you won't even notice. So relax, it's not like you have to write a refresher exam to keep up :)
[1] today I'd get basically nothing in an exam, I don't remember all the memory-rote stuff, like naming the 7 OSI networking levels, or some specific algorithm, or the theory of P vs NP complete etc. But I actually tangentially use that knowledge every day.