Most Common Use of Nulls in 15th Century Cipher Text

[nickpelling]

Yes, l agree.  Any thoughts on sources?

I'm not sure. Cipher historians tend to overfocus on cipher ledgers, because they're such a rich (and often surprisingly diverse) source of information (both technical and social), but they (of course) bracket the whole issue of scribal cipher practice (e.g. nulls, but also homophone usage, and mixing plaintext with ciphertext).

I'd need to look back at the sources. Cerioni mentions lots of letters that were decrypted (presumably centuries) later, but I'm not sure these have been examined from the point of view of practice.