Thanks for your post. I see you linked a previous post in the Community, so I thought I'd relay the same information here!
October, 27th 2015 marked a huge milestone in TeamViewer’s history: TeamViewer has been activated on more than 1,000,000,000 devices worldwide. Due to this, more and more devices are now getting a 10-digit TeamViewer ID.
You can find some more information on the blog post from the day, including the video below
Thanks for the continued support of TeamViewer!
The TeamViewer ID is found in the TeamViewer application after installation.
For more information on how to use TeamViewer, and where certain information is, please see the following support article.
I hope this helps!
well older versions cannot connect to newer ones anyway and unless older versions also get 10 digit IDs (which if the older versions dont support, probably also wont get) there wont be a problem.