There are multiple older translations, but Project Gutenberg only has one at the moment. I'm conjecturing that they used to have a different one (also out of copyright; that's their whole thing), but have taken it down for unclear reasons.
It's also possible that I found a free translation of The Three Musketeers somewhere else, or that I read the same version PG has now and have misidentified it as being different.
There are multiple older translations, but Project Gutenberg only has one at the moment. I'm conjecturing that they used to have a different one (also out of copyright; that's their whole thing), but have taken it down for unclear reasons.
It's also possible that I found a free translation of The Three Musketeers somewhere else, or that I read the same version PG has now and have misidentified it as being different.