A lot of the RSD releases are extremely limited. Last year, there were more participating stores than there were copies of Anberlin's Cities meaning most stores got 1 copy but some store didn't get any. It's not as easy as walking in and picking up a copy.
Lol you obviously only enter record stores on recor store day only. Most stores have stocks upon stocks of record store day releases months after RSD. I bough Cities at my local store 4 months after April last year.