How to pack linked files from referenced NuGet packages

I have a build-properties-defining package that is to be used by all the libraries.
Some libraries may provide a json file, that should be retained when they're referenced by some other libraries and then, ultimately, all the configuration files should be transitively provided to a consumer of a top-level library.

There's a convention, that libraries place their configuration files into an appsettings/cfgs directory.

Currently I have the following in my build-defining package's xxx.targets file

...<ItemGroup><Content Include="$(ProjectDir)\appsettings\cfgs\*.json"><CopyToOutputDirectory>Always</CopyToOutputDirectory><Pack>true</Pack><PackagePath>contentFiles\any\any\appsettings\cfgs</PackagePath><PackageCopyToOutput>true</PackageCopyToOutput></Content></ItemGroup>...

What works when using the target file above:

• when a json file is added to appsettings/cfgs, it is copied to build output by default
• when a json file is added to library's appsettings/cfgs, it is packed into library's NuGet package via dotnet pack
• when a library is referenced, its' configuration files are shown in solution explorer as appsettings/cfgs linked directory and linked files are copied to consumer's output.

What doesn't work:I have library1, that provides a configuration file 1.json. I have library2, that consumes library1's NuGet package:

• 1.json is shown in solution explorer
• 1.json is copied to library2's output on build
• 1.json is NOT, despite my best efforts, included into library2's NuGet package, while library2's json files, lying in the same very directory of output, are successfully packed.

How do I ensure that files, linked from referenced NuGet package, are added to consuming library's NuGet package, produced by dotnet pack?

provided by libraries, are packed into a NuGet package