Gil - I fully intend to replace those but for now they are place holderss - they fulfill the requirements I have: Issued by, for or showing the emperor. Its a bit tenuous for some coins (like those mentioned) but as I care for the history I'd rather have the Constantius II coin for Vetranio than a Vetranio bust one. Its a pretty good story!
There are a couple of other minted 'under X' coins which need to be replaced too. Its unfortunate though that I may never be able to get a portrait of Caesar from his lifetime.
The main issue here is that I would rather get on with filling gaps than replacing ones I have - especially with my budget. I'm taking whatever I can get!
Oh, and it I think its worth mentioning the budget for all this - I have spent no more than £130 so far - including postage (that includes my parents expenditures on it). But to be honest, they have all been worth it - I've had more than £130 worth of amusement from the venture.