It’s really problematic. For a specific example, let’s look at Barrie’s Peter and Wendy. It was published in 1911, so is well below the current 1925 barrier in the US. In most countries he falls into the 70-years-after-death PD boundary, and in Mexico with their 90-years-after-death it’s fast approaching the PD date. But in the UK there’s a specific exception built into law that it’ll never go into the public domain: https://www.legislation.gov.uk/ukpga/1988/48/section/301