Filemaker 12 files have a new file format. It can't open previous versions of FileMaker. It can only create converted copies of the files and open the converted copies. It can't do such a conversion on a hosted file--only a local file so you can't access hosted files from previous versions.
So my statement "YOU CAN'T OPEN ANY SHARED (hosted) FILES UNLESS YOU CONVERT THEM TO VERSION 12" is correct. I will now have to share the files from version 12 as well since you can't open 12 on earlier version.
This is going to make a deployment of version 12 a weekend job since I'll need to change everything over at once.
Thanks for the direct answer.