As shown in PL/I or NEWP, C could have done it both ways, checked and unchecked when really required, e.g. PREFIX(SUBSCRIPTRANGE), PREFIX(NOSUBSCRIPTRANGE).

Likewise regarding the storage for the length, if one is willing to go the way C went down a few years later, declare a pointer and make the array storage be pointer based, e.g. BASED(MY_ARRAY_PTR).