LV 60 Dungeons don't count towards cat book???

[AmiableApkallu]

So why say any dungeon between 51 and 79 if all 60 dungeons are invalid???

Because it didn't say any dungeon. It said, "Leveling Dungeons (Lv. 51-79)." The dungeons in the Leveling roulette in that range.

That said, the whole Leveling vs. High-Level dungeon distinction feels like an anachronism from the ARR/HW era...