Op: Klondike has some vague allusions to how Clan-like things were. On the one hand, you had Truscott setting up a years long spy network with Bugeyes and other surveillance to make sure everything went according to plan for the invasion. And Zell was, in large part, the result of the death of Andery during Klondike.
On the other hand, you had the Coyotes, who were inventing new things to be Clanlike, declaring them as such, and only checking with Kerensky about them later. During the invasion of Babylon, the Yotes almost messed up one of the WarShip cache recovery missions, and then abandoned the Foxes because they went a little honor crazy.
The impression given by the book, IMO, is that the eldest members of the Clans, particularly those with SLDF experience, were far more strategic, and (since many/most of the Khans were of that generation) directed the invasion in a more 'winning is what matters' ethos. The young firebrands were far more True Believers to Nikky's new society.
I don't imagine the CLPS was used very far into the Golden Century, but a liberal Clan could certainly justify it, IMO during the invasion. At least, that's my explanation for why it shows up on the MUL for the Star League in Exile list, and why I included it here.
EDIT: That being said the place to be tricky might be somewhere other than the Khan's personal Heavy Cavalry Star. Definitely worth considering putting it elsewhere.
I also admit that the (fluff) idea of using a base five formation against an enemy expecting 4, with an invisible unit seems very fun, for the sorts of Clans who would lean that way (Foxes, Ravens, Mongeese).
The point about the Crusader is well made. It's both [Ubiquitous] (which I'm making a requirement for duplicate mechs, as a personal rule) and also an obvious ancestor of the Fox. I may need to see if I can squeeze another one in somewhere.
