I was missing only Longspur Blaze and Longspur Scout from my Longspur Collector achievement. I got Longspur Scout from Maelstrom Story Mode with solo running with my level 55 sentinel. Anyways, when I got it, it made Scout updated on Collector achievement and also, made Blaze updated. That was weird. According to game, I had all Longspur vehicles but it was still "incomplete". After that, I bought Blaze from vendor with classic commendations. Even I bought it, it was still incomplete. Now I have all Longspur vehicles on my sentinel but it is still incomplete. Appreciated for any help.