Complex sentence: The works of C.P.E. Bach are known by "Wq" numbers (from Alfred Wotquenne's 1906 catalogue) and by "H" numbers, from a catalogue by Eugene Helm (1989).
Split into simpler sentences: The works of C.P.E. Bach came to be known by their Wq numbers (from Alfred Wotquenne's 1906 catalogue). They are now also known by their H numbers, from a new catalogue by Eugene Helm (1989).