If you read Article V it is a single sentence long. At the part where is says "or, upon the application of 2/3 of the states, shall call a convention" you'll note it does not say, "upon the application within ten years" or "upon the application for the same subject" rather, it states clearly that the only term/condition placed on an application is that it be cast. There are no same-subject/contemporaneous requirements. Why? Because obviously, if the states are going to meet in convention, there is no reason to agree to anything before doing so, it's a non-binding deliberative assembly. Also, there could be a situation where three states want one type of amendment, three states want another type, but upon assembling it's discovered a different amendment altogether will solve both complaints. And that's what an application should be viewed as--a complaint. Once Congress receives enough complaints, it goes to the cleaners. If the purpose of a convention is to build consensus, why would you unnecessarily require members to agree beforehand? If the spirit of the convention clause is to force Congress to legally sanction a discussion about Congress, you would base it on an objective numeric count, that way Congress can't debate whether or not it's time for the call.
Over the years, states being states, have done things a little differently, and these differences in the texts of applications, what is known as constitutional dicta, have become the focus of politicians and political pundits, to confuse people. The only requirement is numeric count and there are hundreds of applications strewn across congressional records.