Just a heads up that this is just something /a/ typeset from the TL I had posted on /u/. The regular typesetter (with the Speedy Sea Cucumber Seal of Quality) will be working on their version with nicer fonts and proper QC and such soonish so please wait for that.
They're really not. For one thing, the original Kase-san series was completely web-based whereas Yamada to Kase-san is published in the Wings magazine. And the lack of chapter numbers only applies to the first series, as they're technically treated more like a series of oneshots with continuity...
As a little translator's note for p4, the original Japanese phrase was "kigen ga ii mitai", but Niji ended up typing 期限 (deadline) instead of 機嫌 (mood).
tldr Some dolt thought it'd be a good idea to merge the first series with this sequel (the latter of which has blatantly numbered chapters btw) and it's made things horrible.
Why did the two series get merged anyway? The original Kase-san and... series and Yamada to Kase-san are prequel and sequel respectively, and unlike the former, the sequel has a clear numbering system for its chapters in its raws.
Depends on what the raws say, but I guess it could be distinguishing 百合 (pure feelings between girls) from simply レズ (girl on girl smut regardless of actual sexuality)?
Just a heads up that the next release will likely be the pre-serialization oneshot. While it is a different beast to what we have now in many ways, there are some familar story beats so there may be potential spoilers for what lies ahead in the serialization.