v5 means almost nothing
its simply a reference tool for dvla to hold somebody responsible fro the tax and any incidents it may be involved in
if you carry out due diligance[hpi check,physically check numbers etc] you have done all you can to buy it properly

even if a previous owner say no to the v5 question letter they will issue unless he can provide evidence he owns it or has had it stolen-as they have to have somebody responsible for it