You don't even need an annual fee. Even a one-time fee is sufficient deterrent to blanket extension of copyright. The old 56-year copyright term used to be sp

You don't even need an annual fee. Even a one-time fee is sufficient deterrent to blanket extension of copyright. The old 56-year copyright term used to be split into two 28-year periods. You basically paid a one-time fee: half at the original registration, then half (adjusted for inflation) at renewal. If you didn't renew, then you got to pay half the fee for half the copyright term. Only 15% of copyrights on books, periodicals, and music were ever renewed. The renewal rates were higher for maps (40%) and motion pictures (50%). Thus, commercially-significant work was protected. However, the vast majority of work (85% of books!) only had an ephemeral cultural value, so the authors chose to take the fee discount and allow their works to enter the public domain. Source: Divide 1977 renewals by 1950 registrations for each category. This is off-by-one (27 years instead of 28) because 1949 and 1978 tabulations aren't as easy to access. That's why I give round numbers.