Like you said, do research.

Anyway I think OP has a point there. They need to either make another version of gaara and call it Gaara [Great Ninja War] and use that in game model while reskin the current Gaara 5th Kazekage because currently he is using the GNW model amd I believe his mystery was developed after he got killed and revived because he didn't use that skill when he fight Deidara. Clip : https://www.youtube.com/watch?v=yNYK58pQi7Q
Or to make thing easier like op said, just remove the the jinchuriki tag and it's done. Also change the cover image for him in Ninja tab.

I did mentioned it in my comment if you can actually read it through. Also consider 3 things : cover, actual in game model and mystery skill. Both actual gameplay model and skill said this is Gaara when he at GNW, only the cover said it is before he his death. So 2 things that actually gameplay related are definitely make more sense than just 1 mere wrong cover.

Further more this version of Gaara was added together with a batche of characters in Kage Submits arc which heavily referred that this Gaara is the Gaara from gnw period.

Enough said I guess.