I am creating several similar assemblies.  The assemblies use parts that are not in my current version of solidworks which is 2018.  When I only one particular assembly open, I saveas and give it a new part number.  Then it asks me how I would want to save the older version parts (saveas, save and open, etc).  I don't want to save those old parts in 2018 yet.  How can I stop this behavior?  It is a recent occurrence.