As you know the datasets are distributed via MDC, and only the last version. Older datasets are taken out of circulation to respect user’s data deletion requests, which are legally binding.
This is currently what you can:
Use the latest datasets from MDC
Provided that your use case is educational/scientific, send an e-mail to commonvoice@mozilla.com explaining your request/use case to get a download link. You should NOT release any model with that data.