Sacrifice at Midnight has not dropped for us once

My friend and I both play PoE fairly regularly and duo often. However, since the Sacrifice of the Vaal expansion was released, not once has a Sacrifice at Midnight shard dropped for either of us.

About six months ago, we became very curious as to why this was the case. I checked the Path of Exile wiki, and it gave details on the drop ratios for the Vaal Construct within Corrupted areas. It said that half of the time a Vaal gem would drop, and the other half of the time a Atziri shard would drop. Sacrifice at Midnight was the rarest of the four shards, having a 10% drop chance (among the shards, 5% overall).

In our guild stash, we have ten sets of the other three shards gathering dust. We've been selling all occurrences of the three we already have because we don't see a reason to stockpile more. By our estimation, we should have found at least three Sacrifice at Midnight shards by now (statistically speaking).

Are we missing something?

Is the Wiki wrong regarding the rarities of the shards? Is there some requirement for getting the fourth shard to drop?

It makes no sense to me that not a single one has dropped for us from any of the dozens of corrupted areas we've cleared in the time since the expansion was released, but there were players who managed to find all four shards and beat Atziri three days after the expansion went live.

The zone needs to be level 60 or higher.

If it isn't working out for you, run your other pieces in the map device and get more midnights that way.