Following the change of management of a site, I need to change the code relating to the Tag Manager of this site with a new one. I was wondering if, once this is changed, the data relating to the period prior to the code change will be available or only those relating to the new code will be visible. I looked for references on the Google FAQ, but didn't find much about it.
Google Tag Manager container changes doesn't affect the data that's already in Google Analytics. If you were to replace the GTM container ID on a website with another one, the GA data prior to the change will be there and any new data coming into GA from GTM will be set by the new container.