Whenever I do /locate in the past dimensions to find a portal hub (since there's the bug with the portals themselves not spawning near the player), I teleport to the coordinates, only to find no portals at all (not even frames). I dig straight down, standing on the same block which I teleported onto. I pass through bedrock without finding anything besides stone, dirt, granite/diorite/andesite, and ores. At least I was in creative mode so I could teleport out, but I can't imagine the frustration if one were in survival with no commands enabled and discovered that the portal hub wasn't there.