Unable to upscale Heirloom items

I started playing again and I’m confused about how heirlooms are working. I’m mostly doing it for gear’s sake as I’m leveling so I don’t have to be so concerned w/it but I wanted to scale some higher and I can’t. I noticed that some end in -4 and some end in -9 (i.e. Heirloom Upgrade Level 3/6 1 to 44 or Heirloom Upgrade Level 2/6 1 to 39). Yet when I buy the corresponding heirloom scabbard for a weapon, let’s say for Hellscream’s War Staff (Heirloom Upgrade Level 2/4 1 to 49), the scabbard to scale it to 50 doesn’t work.

Am I doing something wrong? Is this a bug by chance? How can I upscale these items?

Are you sure you’re picking the right scabbard? I personally have a hard time remembering which overblown name corresponds to which upgrade level. I almost always buy the wrong one, try it, sell it back, and buy another until I find the one I need.

The tooltips have been bugged for a long time, maybe since Shadowlands launched. For the sake of the upgrade items, your level 49 heirloom is essentially “level 50,” so you should be able to use the next tier upgrade on it. I think they made the tier end in 9 so you couldn’t level from x0-x1 with the heirloom bonus in new expansions.