If the required symbol versions are provided by the old glibc version (which is a bit unlikely), it will still work. The internal glibc hash tables are ignored

If the required symbol versions are provided by the old glibc version (which is a bit unlikely), it will still work. The internal glibc hash tables are ignored by the link editor, and most distributions override the link editor hash table default anyway. (What changed is that glibc no longer overrides the distribution defaults.)