All of the Seventh-day Adventist Yearbooks, save for the current one (which can be ordered from the Adventist Yearbook website), are in the online archives. When the current Yearbook becomes a historic Yearbook, its PDF is uploaded to the online archives.
A gap does exist in the Yearbooks from 1895 to 1903, but that is because the Church did not publish a Yearbook during those years. We cannot digitize that which does not exist. However, in that time period, the Church published the information typically found in the Yearbook in the Review and in a periodical called the General Conference Bulletin.