Note that all items are assumed to be appropriately sized for the race using them. If an ogre is using a halfling's buckler it would be no more than a hand guard. If a halfling used an ogre's wall shield it would be a wall...
I look at shields as a subgroup of armor, and consider the lack of IV on their table in HARP Fantasy to simply be an oversight. (Of course that could just be my convenient excuse to make it work) If you wish to go with the ruling that all complete items are IV=5, go for it, I'm not going to argue.
As for a next revision for HARP - that would be a long way off, and likely to include a lot of significant changes, not just minor changes. It would be up to Nicholas if this needs to be included on future printings of the current rules.