When you qualify for an SLC you automatically qualify to sail a monohull no matter what your experience is listed in the logbook as long as your Rank is Barebaot Charter Master Level 3 or above. (The length of the monohull permitted is based on your previous boat length experience logged)
To get be eligible for a Catamaran checkmarked SLC, you must have either a catamaran qualification listed on your sailing resume or a catamaran endorsement. See this article about Catamaran Endorsements and qualifications
(The length of the catamaran permitted is based on your previous boat length experience logged or the length of the catamaran in the assessment)