$99 for 12-months Humble Choice premium/classic plan gift (giftable to self)

I've gifted me the 12 months, and YES, it auto-activates this month.

As javidoom said you will get this month Choice, but you can buy as gift and wait till January Choice (3 days left) and activate gift subscription (as far as I understand gift not expire and can be claimed any time in future, i.e. in February).

I don't think it's an oversight. It's a well-known marketing technique to have the price-sensitive customers jump through the hoops to get a better deal while the others just pay a standard price. That way they can retain both types without lowering the price for everyone = more profit.

Check your coupons - you might have another one for $6 for 6 months valid until June 4th. So it's basically 12 months for $6. And next year there probably will be another promotion. So I'm not sure if it worth buying it now. But yes, you can use it after $6 deal expires, just don't redeem it before that or it'll cancel $6 deal.