I maxed out last seasons mission pass, but never used a gold ticket. Am I now too late? I used one on the current season, and when I go to use another it says it activates for the current season, and when I go to unlock the items in the previous season it brings me to the SG store to buy a gold pass. If I use this other pass will it let me get last seasons items? Or will it just be used twice for the newest season

If you try to use a second pass, it will just tell you you cannot use it. Unfortunately, you missed the chance to get the Gold rewards for the previous season.