Different use years can be a pain if you plan to combine the points from them to book a vacation. You'll need to call MS to do it.
It's just simpler to manage if all your contracts are the same use year and titled exactly the same so that they can behave as though they are one big contract. This is the best arrangement if you need or want to book online, too.
Different memberships (and different use years always mean different memberships) behave as though they belong to two different people. They work best if you don't plan to use them together. For example, you always stay at BCV in October for F&W and at the VWL in early December. You only use your BCV contract for the BCV stays and only use the VWL contract for the December stays. (Both require 11 month booking to be sure of getting exactly what you want).
IMO, it will be worth waiting for a December use year to match the one you already have. Good luck!