Quote Originally Posted by neuroanatomist View Post
In the case of the lenses mentioned, the Tamron 17-50 non-VC uses LensID 161, which is Canon's code for the EF 28-70mm f/2.8L - and that lens is on the above list of lenses with limited compatibility. Likewise, the Sigma 18-125 uses LensID 6, which is Canon's code for the EF 28-70mm f/3.5-4.5, also on the above list.

To fix this issue, Canon would need to update the 70D firmware to deliver full compatibility with those old lenses.
The lenses don't show up in camera as the wrong lens. They show up as just the focal range. Perhaps I don't understand your comment?

I was mostly trying to give real usage examples of how these 3rd party lenses perform.