In addition to this, does tiger and tiger-backend 8.9.0 need the latest version of GDCN to work correctly?

Hello Justin, I just tested a simple

<Headline />

component from the GoodData.UI version 8.8.0 under the GoodData.CN CE version 1.6.0 and it works fine. Regarding the latest GoodData.UI version 8.9.0, I tried to upgrade and again run against GD.CN CE 1.6.0. Again, I was able to render a simple

<Headline />

component without any issues.