From Emmanuel Music (“Bach Reconstructed”):

A reconstruction of Bach’s “third” passion will be presented by Emmanuel Music for the first time. The St. Mark Passion’s missing pieces have been carefully reconstructed by modern scholars and composers. This completed presentation will be new to many ears, and a welcome addition to the two great Passions we know and love.

It seems very likely that the St. Mark re-used and adapted much music from the Trauer-Ode, BWV 198.