The first screenshot is from the Pilot, Part 1. -- The whole tattoo we are familiar with is shown.

The second screenshot is from Stranger in a Strange Land, when Jack is being held hostage by the Others on "Alcatraz island." This is well after Achara did his tattoo. Again, Jack has the whole tattoo we know well.

The last screenshot is from Stranger in a Strange Land, the moment when the Thai boys lift his shirt. A moment that happened before the first two screenshots, yet half of the tattoo is missing. Where is the Christmas-tree-looking thing with the green 5?

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"Helen, do you remember that authentic Australian walkabout I told you about?"