The ebooks we produce are entirely in the US public domain, including metadata and any other files. Unfortunately there are basically no good fonts released under the CC0 license. (Most open fonts are released under the OFL license, which is not the same.) Therefore we don't embed any font files, except for Standard Blackletter[1] when necessary, which is a font we developed especially for our use based on public domain specimens, and released via the CC0 license.

[1] https://github.com/standardebooks/standard-blackletter