Considering Nick's broadcasts had three R&B segments per half hour and Nick Mania lasted two hours, they could have included two six-chapter storylines.
That's how they are in syndication...
The syndication package for R&B contains the first two seasons with a R&B segment, a Fractured Fairy Tale (occasionally alternating with Aesop and Son), Mr. Know-it-All, Mr. Peabody (occasionally alternating with Dudley Do-Right), a second R&B segment, and Bullwinkle's Corner; the other seasons were presented with a R&B segment, Mr. Know-it-All, a Fractured Fairy Tale, a second R&B segment, Bullwinkle's Corner, and a third R&B segmetn... after Nickelodeon, Seasons Three and Four were dropped from the syndication package, so only Seasons One, Two, and Five are seen in reruns.
A lot of cartoons are like that, Drtooth can explain this better than I can, but the FCC requires a classic cartoon have a minimum of 65 episodes to be syndicated in reruns, which is why you only see certain episodes and seasons of some cartoons, but not others... like with the 80s version of
Alvin and The Chipmunks, the first five and a half seasons (exactly 65 episodes) are syndicated in reruns, but not the other two and a half (but that's okay, those were weaker seasons anyway).