This is everything I can think of about libraries management. There have been a lot of changes over the years.
Objects, doors, windows, lamps, skylights, labels, zone stamps, section/elevation/detail markers, door/window/skylight markers, change markers, drawing titles, patches, databases, list schemes, properties, textures, surface definitions, background images. Not much, really.
Attributes, work environment schemes, model view option combinations, graphic overrides, renovation filters, saved find & select criteria, view sets, schedule schemes, dimension standards, DXF-DWG translation settings, element transfer settings.
More on what libraries are where can be found here. Version numbers in library names (LIB20, e.g.) will change when the version of Archicad changes.
From the carrot (2 Libraries): 1 Rill LIB20. It's located in the Master LIB 20 folder. Don't load the whole Master LIB folder. Use the most current library relative to the Archicad version you are working in. Most of the time, I only do active maintenance on the most current version of the library. When you migrate a project to a newer version, use the Library Manager to unload the old Rill LIB and load the newer one. Don't load a library with a higher version number; some parts will certainly not work.
From your local disk: For Archicad 20, Archicad Library 20, the entire folder. Its location is Applications/Graphisoft/Archicad 20. This naming pattern has been consistent for many versions, so I expect you will do the same for future versions.
So we all have the up-to-date library all the time. I update library parts frequently.
Because that's where Archicad expects to find it. There is absolutely never any reason to move the Archicad library or load it from somewhere else.
No. Again, I update library parts almost every day. If you are using a local copy, you are out of date. You could copy them every day, but this isn't any faster than loading them directly from the server. We sacrifice a few seconds of loading time for the benefit of having one consistent library for everyone. tl;dr: No.
Yes, in the lower left corner of the Library Manager, there is a dropdown attached to the Add button. This shows previously added libraries. No matter what machine you are on, you can always choose the Rill Library from there.
If you open a project and the Rill Library is missing, it's probably because the project was worked on outside of the office, so the Rill Library had a different path. Use the dropdown to select the previously used path.
Since AC14, Archicad has had the ability to consolidate the Archicad library. This means to load the current version of the AC Library, and load special migration libraries of parts from previous libraries which are placed in the project, but have been removed from the current AC library. This way you get the new AC Library, but your old placed parts should not be disrupted. In any Archicad version upgrade, most parts are un- or slightly changed; those parts will just work, even though the name is different because of the version number (Armchair 20, e.g.)
In AC18 and later, on first opening a project from AC17 or earlier, you will get a dialog box offering to perform this migration and consolidation process automatically. Do it. If you skip it, you can do it later by clicking the 'consolidate' button in the library manager. After migration, you will see the 'Archicad 18 Library' along with the 'Archicad Migration Libraries'. (In earlier versions, the separate version libraries were listed individually.)
Migration only applies to the Archicad Library. After migration, the 'consolidate' button is no longer shown.
When opening a project in a new version, always use the Library Manager to switch to the most current version of the Rill LIB. This is separate from the AC Library process above. Again, I only actively maintain the most recent libraries. (Bug fixing is different.)
It is part of the project file. It is shown in the Library Manager, but it is not an external resource. Parts in the embedded library are not available to other projects (unless they are hotlinked). Use the embedded library for parts which are highly specific to the current project. Often these are one-off slabified objects and 2D patches. If you think you will use a part in another project, save to an external folder.
Tell me. Wait, back up a little. Before you tell me, reload the libraries. Some apparent problems are caused by my fooling around with things, and you just need to get the latest version of something. Tell me even if it's an Archicad object; I can probably help you work around its issue.
Bad-behaving objects often cause errors that show up in the report window. The report window should be kept undocked (not in a tab), so when it is activated you will notice. Don't ignore the report window. We have a much better chance of finding the problem with an object if we notice the problem right when a change was made.
There's a command on the File -> Libraries and Objects menu. We have a keyboard shortcut for Reload, which is Ctrl+Opt+L. The Library Manager is Cmd+Opt+L. The default Archicad work environment doesn't have shortcuts for these items, like a caveman.
Make sure the carrot is mounted. If it isn't: In the Finder, Connect to Server (Cmd+K). The server's address ends in 91.
Do not ignore missing objects. These directly affect the project itself. (Exception: Sometimes a zone stamp will be reported missing when it isn't, it was merely in use in the previously open project. Bug. Still! For so long.) Tracking down missing parts in very old projects can be a chore, but I know you can handle it. Ask for help.
Generally, do not ignore duplicates. Try to resolve the issue. Ask for help if needed. If you have duplicate objects, you can't be sure that the one that gets used is the right one; it may be that the other one is more current.
You will often get duplicates when opening an old project. If you determine that the duplicates are from the Archicad library, you may be able to let it go. If the duplicates are from the old Smart Parts library, you can definitely let it go; those objects have never changed.
Another problem with tolerating duplicates is that you get used to seeing the report pop up, and you ignore it, and when it says something important you've stopped paying attention.
Not the name. Library parts have an internal identification number which is usually hidden from the user called the GUID. It is this number which has to match in order to have a duplicate reported.
If you Save As on an object, the new copy gets an entirely new GUID which cannot be modified by the user. Even if you don't change the name. Archicad is just fine with having multiple objects of the same name, as long as the GUIDs are different. They always will be different, as long you do normal saving and saving as of library parts.
You can create library parts with identical GUIDs, but you have to go out of your way to do it.
The good thing is, you can change the name of an object file in the Finder, and since the GUID is not changed, placed objects will not be disrupted. The name will change in place automatically. (This is how Armchair 19 can turn into Armchair 20 without disruption.)
Window -> Palette Display -> Show Library Loading Report.