Both tags are used to describe a larger than average mons pubis, though not abnormally so, yet we should only use one, yes? I've seen "fat mons" used on the likes of Gelbooru but I can see how that can be more misconstrued here due to their being a greater focus on pokemon and "fat mons" may come off as something else entirely, yet "Puffy Pussy" plays off of the well used "puffy anus" tag. At the same time, "puffy pussy" isn't completely accurate and the tag is actually normally used to describe the entire mons and labia being enlarged, usually by "pussy pump" in relation to the highly underused tag "Pumped pussy".
So perhaps we could have some of the users and hopefully admins weigh in.
Updated by Ratte