Sorry, I don't have any clear answer.
My guess is that Costco does not hire delivery people. Costco has people at LG shipping products for them. And those people who distribute LG products will hire delivery people (whoever they like). That's only my guess.
Also, if you order a range, your item may or may not be available in your area. So, that's another variable. So, if they say 2-3 weeks, I will trust it actually requires 2-3 weeks.
I don't know about confirmation email. Did you buy oline? Then can you check from website? They should tell you when it will arrive. Hm…
Again, sorry for not having any clear answer.