If they aren't used for all of those, then they are still paid. In the 80's, guarantees represented more episodes and there were a lot of actors who had some pretty big 'pay or play' contracts. That meant that they got paid whether they worked or not. There are people on staff who's job it is to make sure that all contractual obligations are adhered to. It is simply a cost of doing business.
All soaps employ people who make sure that the actors are used the minimum of days per week.
The HWs also are very aware of who needs to be used and how many times per week are their minimum commitment. All actors under contract have the show they are signed to as their priority. A contract can stipulate the type of work an actor can or can't pursue during the duration of the contract as well. Most have a standard 'morality clause' that prohibits the actors from posing nude, for example, while they are under contract. Many have posed partially nude during their time on soaps, which is fine.