I have written a little software package to decode v23 encoded files. It can be adapted to support parity. It can back-track in case of parity/framing errors.

Another neat feature is the timed octets output which preserves timing information.

https://github.com/Casandro/v23_tape_recovery

There will be a talk about Bildschirmtext at this years HOPE conference.
https://scheduler.hope.net/hope2020/talk/XGCTBB/

It’ll be streamed here https://www.hope.net/stream.html and after the event there will be a recording.

https://archive.org/details/hopeconf2020/20200729_1800_Bildschirmtext.mp4