Use Ansible include_tasks with tags on the sub-tasks

Q: "Is it possible to have Ansible just "know" what tasks are within the include_tasks block and pull the applicable tags?"

A: No. What is inside included task will be available after the control-flow reaches the include_task statement and the file is included.

Q: "What's the best practice for achieving this goal?"

A: Use import_tasks. Imports are read when the playbook starts.