Yeah, the "lost, defective pearl" line always stuck out to me too, not only because of the phrasing but because there's no way she'd know/remember Pearl personally. And the way Jasper looked down on the Gems, but seemed to have a more personal vendetta against Rose, makes me feel like how numerous Gems are varies. Like pearls and amethysts could be really common, while there's only a couple, or even only single versions of Rose and Jasper. Kinda like Brave New World, and tonnes of other media, I'm sure.
I also wonder if the position of the gem is meaningful to role. There's only so many places gem can go, really, and we've already seen doubling-up with the forehead placement between Pearl and Periodot - and they kinda strike me as a bit similar, being all about order, but also switching into manic mode when things are out of order, etc. So maybe forehead = brainy? I also wonder if Yellow Diamond is gonna have her Gem as the crown of her head, for an eerie bald woman look, and also as a crown allusion. The Yellow is also ominous: suggests there's more than one Diamond to worry about.