did they open access their model weights?

In that instance it wasn't really training, it was crowdsourcing the transcription. Rechapta would pull out a word from their book archive that the OCR failed to recognise, and if many people identified it as the same word, it would be archived. Now that rechapta has been purchased by Google, the archive and the transcriptions are available on Google books.

They stopped doing this once ai became more effective than rechapta for book transcriptions.

Modern chapta actually is about training models. But old, classic rechapta was really just about book transcriptions, and those are available.