Plain and simple...
If you do not have to remove building or structure finish to get to the end of the sleeve or chase, it is NOT CONCEALED. The major portion of the run may be CONCEALED... but if one or both ends are not behind a finished surface that has to be removed to access the sleeve or chase, the sleeve or chase is EXPOSED as far as the fish rule is concerned. The fish rule applies only where you have to remove some of the building or structure finished surface in order to fish the cable. A built-in sleeve or chase is just does not meet that criteria. It [typically] already has access to one or both ends; no building or structure finish has to be removed for access. You cannot run NM in that sleeve or chase unless you secure it at intervals not exceeding 4.5'. Doesn't matter whether you fish it through or not.