Access has been somewhat reluctant to make BeOS-related material available in the past. For example, they did provide access to the BeOS API documentation (called the Be Book) to the Haiku project, but only under a restrictive no-derivatives license (see [1]). This has caused some pain the past, as extra care must be taken that Haiku's API documentation, the Haiku Book [2], is not a derivative work, so everything had to be rewritten from scratch, even documentation for parts of the API that are largely unchanged.

[1] https://www.haiku-os.org/legacy-docs/bebook/LegalNotice.html

[2] https://www.haiku-os.org/docs/api/index.html