I understood it this way:
You are a caster of appropriate class and level for that scroll: no roll.
You are a caster of the appropriate class for that scroll but of a lower level: you roll.
The "otherwise" is for the level prerequisite.
Maybe I am fooled by the knowledge of the old 3.x rules.
You are a caster of appropriate class and level for that scroll: no roll.
You are a caster of the appropriate class for that scroll but of a lower level: you roll.
The "otherwise" is for the level prerequisite.
Maybe I am fooled by the knowledge of the old 3.x rules.