Just ordered a new iMAC (27 inch, retina 5k, 3.3 GHz processor, 8GB memory, 512GB flash storage.....I want to upgrade the memory to 32GB,.....contacted Crucial and first question asked on chat was the model number....obviously don't have it since order is in process...was asked if it was a late 2015 model.......i would guess that the machine when delivered with be that model since i believe that is the most up to date model. Is this a correct presumption on my part or should i wait to get the machine to verify the model before ordering the memory upgrade? Thanks for your help.