Currently building release/6.01xx doesn't produce the template packages. This is because IsPackable is set to false for preview and servicing releases as described here. This doesn't work well for .NET source-build which needs to product the entire product for every build (e.g. previews, rtm, servicing, etc).

Would it be amenable to conditionally build all template packages during source-build (e.g. Condition="'$(DotNetBuildFromSource)' == 'true'")?

Currently source-build treats these packages as text-only packages that are checked in/reverse engineered. This solution is not ideal as it requires manual updates, is a maintenance burden, and in general is problematic.

This issue is similar in nature to dotnet/aspnetcore#39471.