Warrior Cats has several Early-Installment Weirdness, especially in the first book.
- Each Clan keeps mostly to itself and doesn't know much about what's going on elsewhere in the forest, and the other Clans' territories are generally a mystery to them. Tigerclaw freaks out in the first book when they take Yellowfang as a prisoner because he thinks that now ShadowClan will know where the ThunderClan camp is, and that they'll need to move, while in later books (even ones that take place around the same timeframe) they actually visit each other's camps on a fairly regular basis. Likewise, in the first book, they say a few times that "that cat must have been killed by an enemy patrol" and just forget about it — most notably the ShadowClan leader's death — when later on such an event would be huge news and they would actually confront the other Clan and try to figure out what happened. This is probably partly because since the first book they've established exact rules for the previously-vague warrior code, one of which forbids killing except for rare circumstances.
- The terminology changes a bit, such as the way the cats use hyphens and capitalizations in words (i.e. "Clan mate" becomes "Clanmate"). Also, the first book uses the word "queen" for any female cat, but later on it only gets used for females currently pregnant or nursing kits, and "she-cat" becomes the general word for "female".
- The Clans are a lot more formal early on; in later books cats refer to parents by their actual names rather than calling them "mother" or "father", and in the early books there is almost no use of slang such as "cool". In contrast, the Gatherings in the first series tend to be different groups of cats mixing and talking about current events — for example, a senior warrior talking to a group of apprentices, or a young warrior joining a bunch of elders and medicine cats in a discussion, while later it's mostly cats sticking with their own age group and gossiping.
- Mates aren't, for the most part, treated as major relationships in the first series, and it is mentioned that warrior fathers don't stay close to their kits (with one or two rare exceptions). In the third series, one cat who has kits as the result of a one-night stand (which in and of itself is rare later on) is criticized because he doesn't want to play with his kits, and in the third and fourth series especially everyone gossips about young couples and young cats talk about who they like.
- Early on, cats are rarely mentioned by name unless they actually have speaking lines in a scene, and sometimes not even then. In The Prophecy Begins, you're likely to see something like "Tigerclaw and a patrol of warriors were leaving the camp" while in Power of Three or Omen of the Stars it would be more like "Bumblestripe, Thornclaw, Cinderheart, and Ivypaw were leaving the camp on a hunting patrol". Cats at gatherings and in battles are also usually just described as, for instance, "a silver tabby" or "a dark queen" more often than they are named, generally giving the impression of larger and less tight-knit Clan societies than later becomes the norm. Kits get this treatment, too, leading to the odd effect of cats (in the first three books) not seeming to have names at all until they're apprenticed (with Cloudtail seemingly being the exception due to the circumstances behind his joining ThunderClan) .
- The timing of cats' apprenticeships is weirdly off in series one, and their general ages. This is sometimes due to retcon, but it still leaves The Prophecy Begins arc very weird timing-wise, especially when it comes to kits and apprentices. Ravenpaw refers to Sandpaw and Dustpaw as being apprenticed for longer than he, Graypaw, and Firepaw, despite the fact that he and Dustpaw are littermates and should have started training at the same time. Fireheart and Graystripe become warriors before Sandstorm and Dustpelt, which isn't that odd considering they'd just done something heroic, but they'd only been training for three moons at most. Thornclaw and Brightheart start their apprentice training in the book after their siblings Brackenfur and Cinderpelt do, for no discernible reason. Cloudtail also starts his training before his foster siblings Ashfur and Ferncloud, despite the fact that he is younger than them, being born a book after them.
- The Dark Forest was originally treated as purgatory where cats endlessly walked alone in a starless, prey-less forest. It was later changed into something more social, where the Dark Forest cats interact with one another and even train together.
- In Into the Wild, six-moon-old cats like Graypaw and Firepaw are referred to as kittens (as, in real life, 6-12 month olds are considered kittens). Future books make a clearer distinction between kits (0-5 moons) and apprentices. The terminology is also off as the books use "kit" rather than "kitten". Into the Wild makes reference to "kitten-cough", which is never referred to again and stands out due to its usage of "kitten" over "kit".
- In Into the Wild, Bluestar laments about how "never before have we had so few apprentices in training", since there's just Dustpaw, Sandpaw, Graypaw, and Ravenpaw before she invites Rusty to join the Clan. Books taking place both before and after Into the Wild show that four apprentices at a time isn't at all out of the ordinary.
- In Fire and Ice, Tigerclaw suggests that Darkstripe and Longtail be given a second apprentice each, and Bluestar replies that she considered it but had reasons for deciding against it. Aside from one cat later asking to take on the she-cat he likes as a second apprentice — which is mostly played for laughs — there's no other reference in the series to cats being the official mentor to more than one apprentice at a time.
