The no data is irrelevant to anything else in the file.
The option index is used for default options that would come with that piece of armor every time. For example, you will notice that the level 20+ armors use the option fields to add the + guard, block etc. for equipment that is +4 or higher. It is also used to assign the stats to legendary gear.
The minoption - maxoption fields are used to assign stats when an item is generated as magic-noble-divine.