It's been around for more than at least 100 years.
It's mentioned in the FSI Cantonese course (widely available online).
And it's mentioned in quite a few of those out-of-copyright dictionaries from the previous turn-of-the-century that they have for free download at Google Books, archive.org, & other sites with public domain books. And not just in Cantonese, but, other Chinese dialects as well. The l/n thing.
Kobo.
It's mentioned in the FSI Cantonese course (widely available online).
And it's mentioned in quite a few of those out-of-copyright dictionaries from the previous turn-of-the-century that they have for free download at Google Books, archive.org, & other sites with public domain books. And not just in Cantonese, but, other Chinese dialects as well. The l/n thing.
Kobo.