That's working as intended. The season passes were going to be added with a lag to the Monument to Seasons Past kiosk, with the Ash & Iron pass being added when the June 9th update (Shadow and Order - now cancelled) launched. Bungie haven't announced if that'll still be happening yet, but for now - to get New Malpais right now you have to have the Year of Prophecy edition. Best bet is to simply wait until June 9th if the articles over the next 2 weeks don't mention it and see if you they add the Ash & Iron reward pass to the kiosk; you would need to buy the archived pass to access the items but it costs a few hundred silver.