But suppose the insurance company isn't involved, ie it's not a requirrment? And suppose the club rules simply state that you can't fly solo after 28 days, but need a competent pilot in the other seat. In other words, they're not saying you can't be PIC, just that you need a safety pilot
In that case then you can be PIC because nothing says that you can not. Unfortunately, that is not how most clubs operate.
Clubs (and anyone who owns an aircraft) can decide the club rules to suit themselves. If the club rules do not require a checkout with an instructor when no longer current eg more than 28 days since last flight the that is up to them.
However, the safety pilot system can lead to two friends simply saying that each was being a safety pilot to the other and thus removing the safety element that the 28 day rule was trying to acheive.
Regardless of the system, the person who is designated the pilot in command pre-flight is the pilot in command and they log the flight as such and just as important, no one else in the aircraft can log it as pilot in command.
Regards,
DFC