Heirloom drop rate apex legends

You've just pretty much summed up everything that is known by anyone except for Respawn.  One can surmise from the relative paucity of anecdotes reporting getting shards before pack 500 that the odds are extremely low.  People who think there is a 1/500 chance of getting shards don't understand how the system works, and those who say that the odds go up as you approach pack #500 are likewise deluded.  Pack #499 has just as little chance of pulling shards as pack #1.