From a quick glance I'm guessing that Planet eBook is just repackaging Project Gutenberg or PG Australia/Canada titles, or possibly even Internet Archive OCRs. A commenter below mentioned that italics in a book are in all caps, which is a common transcription affordance in PG texts. It seems they aren't proofread either, since on page 1 of Huck Finn there's a glaring OCR error that doesn't occur in the PG edition ("narra- tive"). And it looks like the PDFs have a Planet eBook watermark on every other page.
One of the goals of Standard Ebooks is to create ebooks that are commercial-level in quality, which after a glance I would say these are not. Our volunteers spend many hours making sure each ebook we release is a high-quality specimen in every way. And you don't get a watermark either.
We're always looking for contributors to make new ebooks. It's a satisfying effort because it takes a lot of different skills: HTML/CSS, command line/UNIX philosopy fluency, attention to detail, an eye for spotting typos, an interest in literature and fine art (for our covers), and more. If you'd like to work on an ebook to release to the world for free, send us a note!
See this simple comparison of what the metadata looks like for the same book (Kidnapped) - https://gist.github.com/captn3m0/ec44b93636b83c1b9f78bfc64a8...
However, due to how both these efforts are treating copyright - planetebook seems to have a better coverage of newer books (standardebooks doesn't have 1984 for eg).
(On SE we have a warning that you need to check your own jurisdiction’s public domain laws; you aren’t legally allowed to download Peter and Wendy in the UK for example.)
In the US, the public domain system is different: works enter the public domain 95 years after the initial date of publication of that work. 1984 was published in 1949, so will arrive in the US public domain in 2044. For the next 24 years it’s illegal in the US to download a copy of the book that’s free by virtue of being in the public domain in a different jurisdiction.
This is a bit of an extreme example, as Orwell died just one year after 1984’s publication. In other situations it can work in reverse. For example, Thomas Mann died in 1955, so his works will typically enter the public domain in 2025. However, Der Zauberberg was published in 1924 so is now in the public domain under US law. This (among works by other authors) lead to Gutenberg being blocked in Germany as they weren’t willing to build a geoblocking system.
At the end of the day, if you want to stay legal (big assumption), it’s your responsibility to check PD in the jurisdiction you’re in. Going just by what websites claim is in the PD is not the best idea.
It's more complicated than that. Works published from 1978 or later (when the 1976 Copyright Act kicked in) is life + 70 years. Works published before then are 95 dates from publication.
Actually, it's more complicated than that: for post-1978 works, life + 70 is for works of individual authors, 95 years is for works of corporate authorship.
Copyright law is a maze whose rules have changed numerous times over the decades. Here's a pretty good flowchart for U.S. copyright: https://www.sunsteinlaw.com/copyright-flowchart