Dragons and Spellcasting

[Arakune]

A dragon wants to advance in a spellcasting class, what it happens to it's innate sorcerer ability?

Or what happens when a dragon picks a prestige class without strict requirements like "need X wizard levels" and just need "ability to cast Nth level Arcane Spells".

[Coidzor]

It counts as a higher level sorcerer.

A dragon with Sorcerer 3 casting and 5 levels in abjurant champion will cast like an 8th level sorcerer

However, a Dragon with Sorcerer 5 casting and 10 levels in Cleric will have sorcerer 5 casting and cleric 10 casting.