Some people believe that this newly defined right entitles them to recover control of their blogs, published long ago, with access (account name and password) long forgotten. A few such people even have blogs owned by "legacy" Blogger accounts, never converted to Blogger / Google accounts.
Nobody has the right to unilaterally take control of a blog that may belong to somebody else. If you cannot prove yourself to be the owner of a given blog, Blogger Support should not provide to you control of that blog. Whether you want to delete a blog, or to change the content, you have to prove ownership of the blog.
So called "legacy" blogs are a concern, because even Blogger Support cannot authoritatively identify all "legacy" accounts. All that they can say is
If your blog was created before 2007, you may have a "legacy" Blogger account.
More properly, since some blogs were converted transparently (without realisation of the owner), they should say
If your blog was created before 2007, and never converted, you may have a "legacy" Blogger account.
The "legacy" account conversion took many years - and everybody was given many months of warning, to get their accounts converted. This was not an overnight process.
All that you can do is to try to convert your Blogger account, and see if you get control of your long forgotten blog. Even if converted, though, you have to be able to prove ownership of the account, once it's been converted - just as you have to prove ownership of any Blogger account.
Too many people try to steal ownership of someone else's blog, by claiming to own the blog - but conveniently forgot the account name or password.
Since there are more people working on their blogs (maybe not today, but sometime in the past), than are trying to recover control, people trying to recover control (or to steal someone else's blog), are going to get less support.
The term "actively working on their blog" implies no specific activity level. A blog, published once, 10 years ago, is just as valid as one published once daily for 10 years.
Blogger blog owners are entitled to the same courtesy and security - as long as each blog owner acts responsibly, and remembers the account name and password of an owning Blogger account. Similarly, blog owners are entitled to Blogger not providing clues, to blog thieves, that could assist in blog theft.
If Blogger / Google does not agree with your claim, and if you believe in the right to be forgotten, you hire a lawyer, and get a court order. Let the courts decide your special rights.