As I understand Octopus has no access to a nuget package to be created in the scope of current build.
So if there is a Octopus step in end the of the build it will create a release ver. A containing nuget package ver. A-1.
A question here: how to configure TeamCity to publish the latest build/package?
You need to create a second build configuration with a snapshot dependency on your ‘build and package’ configuration. By using a snapshot dependency you will ensure that all the artifacts from the earlier build configuration are available.
See the section “Triggering deployments from TeamCity” in the TeamCity Integration documentation.