Polymorphic persistence of RWCollectables is not affected by the addition of the new class RWStringID. Existing files can still be read using newly compiled and linked executables, as long as the old RWClassIDs are unchanged. New classes that have RWStringIDs may be freely intermixed with old classes. The storage size of collectables that do not have permanent RWClassIDs will reflect their larger space requirements, but the storage size of other RWCollectables will be unaffected.

Note that collections containing RWCollectables with the same RWStringID have that RWStringID stored into a stream or file only once, just as multiple references to the same RWCollectable are only stored the first time they are seen.