Yes I know this after extensive googling and 4 days of restoring, re-immaging and so on. In addition you can not restore a prior backup that was saved at a down level iOS version. I MUST restore a iPad 10.3.3 backup SOMEWHERE to retrieve backed up messages. I currently have a iPhone 5 (10.3.3), MacBook Pro, iPhone 6s and also a 5th Generation iPad which can NOT be downgraded to 10.3.3 because A 10.3.3 does not support iPad 5th Generation and B Apple does not have signed OS any longer for prior versions... I have spent days learning this.
if anybody knows a 3rd Party Tool that can let obtain those message please advise. It's extremely important to obtain the messages from that backup. I thought I was golden as I have a iPhone5 at 10.3.3 but messages do not transfer from iPad backup. Ayygh carumba.