You cannot have two different cameras in different scenes, with the same name.
All data-blocks are stored in a single “main” data-base of the active file. That’s what you see when putting the Outliner into the “Blender File” display mode, it shows you all data-blocks in the current main data-base.
This is quite different from the scene-graph design other apps use!
You can then create multiple scenes and use data-blocks into it, but the data-blocks are still in the main data-base. You just add usages of or references to them. All data-blocks must have a unique name per type, per file (not per scene).
(You can end up with duplicate names through library linking though, a common pitfall in Python scripting.)
So what you need to identify a data-block uniquely is the library name + the type + the name. We use that internally to identify data-blocks too.