Idle's last release the gaon and hanteo were matching (funnily, hanteo was slightly ahead). They only recently shipped some new Gaon recently.
Smaller groups also match. I feel you should probably cast a more extensive net before making absolute statements.
No. Hanteo is hanteo certified sellers selling direct to customer. Gaon certification is shipping - SM store is Gaon certified. They sell to say Ktown4u (as just a general example), and that's a Gaon sale. Ktown4u has yet to sell that to the customer. It's possible to have Hanteo above Gaon.
There are Hanteo certified customers outside of Korea. They're a completely separate entity measuring direct sales.
Funnily enough, all the commentary now that this has been pointed out is "oh everyone always knows". Funny that pointing out what "everyone knows" is getting a pretty hostile reaction.
It's not about your faves, it's simply that labels are using stock sales or production runs as "pre-orders" both *technically* true in the sense they are order to be shipped, but disingenuously presented as sales when they are yet to be such. I'll say the same no matter who group is, but this is probably the most recent example and honestly, the most egregious.