I'm surprised to see them so close since recent discussions made me believe Phantom Seer was a bit higher than that.
The numbers we had prior to this for PS vol 2
was higher. Initial Shoseki estimations had it at ~16k for week 1, 5.6k for week 2, and 2.5k for week 3, that's way higher than the monthly number we have. Even if we go with Oricon for week 1 (13.8k), that would still put it at 22k around week 3.
I honestly believe the 22k Shoseki gave to vol 1 in December was greatly inflated, because it just doesn't make sense. Vol 1 was estimated to have sold around 14k during the first two weeks, then disappeared from the weekly rankings completely for the rest of the month, and only sporadically showed up in the daily rankings after the reprint on 12/22, yet somehow ended up with 8k more in the monthly estimates. Vol 2 monthly estimate seems a lot more believable, given what we know.
Another thing to take into account is that Shoseki leaves out several key retailers like online bookstores and comic specialty stores (Amazon, Animate, etc). PS vol 2 was sold out on Animate online store and Amazon like a week before release, was briefly restocked, then sold out on both platforms again before the reprint was announced in the magazine. I expect PS to do a little better at Animate due to retailer exclusive bonus, which Roboco didn't have.
All of this to say take Shoseki estimates with a grain of salt because we just don't know for sure
