In TBC the levels for classic dungeons have changed but this is not reflected, bulletin board still showing old levels.

As reported by dankindoughnuts:

https://70.wowfan.net/en/?zones=2.0#0-2 1 is a list of the new level ranges. you can confirm these yourself in-game with the summon stone level ranges.

https://wowwiki-archive.fandom.com/wiki/Patch_2.3.0 <- also states old dungeons had level ranges changed.