First thing is that brands do come and go (like GRP) or change from manufacturer (Ninja, IDM etc). Exhaust from such brands do disappear automaticly because the different made engine needs a different exhaust.
Indeed a lot of exhausts are renewed on the list, even the 1st 3 chamber 9901 is on the list. Today there is no homologation but registration which need to be renewed every 1 or 2 years.
But these are only for EFRA events and a lot of countries do use this list. But outside europe or even with a lot of races within europe these pipes are still used (like the 2013) so if the need is high they still will be produced.