It is limited only to those who hav has access to your work. Once published the copyright should be registered. Copyrights registration in itself is not comples nor expensive. See the Copyright Page this Forum. It is not a question of registration, it is important to know what you have and what can best be done to acheive what you want.
Enforcement requires registration.
There are published and unpublished copyrights. The unpublished is as I understand it not of much value. It is limited only to those who hav has access to your work. Once published the copyright should be registered. Copyrights registration in itself is not comples nor expensive.