IIRC, The flight recorders are tested by Boeing before delivery to the customer. Planes undergo several weeks to a month of tests by Boeing before delivery and sometimes undergo even more testing by the customer after delivery.

Most likely, the part is pulled for maintenance and its not properly recorded. If its not properly recorded, the plane can be put back into service without the part that was removed.

Air Canada Flight 143 is an example of maintenance records not being kept properly. https://en.wikipedia.org/wiki/Gimli_Glider