For example, a Warlord's Plated Belt has a +1 armor by default. Which should mean you can't add more by imbuing, but I just found one with a random bonus on it.

A "Warlord's Plated Belt +3" says it has a +3 armor bonus (I checked, it really is +3 not a total of +4). But did the random bonus overwrite the default or add to it? Could a Warlord's Plated Belt +5 show up as a random version of this item?
Thanks