At the end of Primer, we know that
there are 3 permanent Aarons: the one in the attic (“Primer” Aaron), the one who left (“Hooded” Aaron), and the one who goes through the story (“Earpiece” Aaron).
“Primer” gets locked in the attic, thus “Hooded” (and later “Earpiece”) wouldn’t be able to exist if — like in most on-screen time-travel — he needs to enter the fail-safe again on the second Thursday, especially considering that Hooded leaves and can’t go back to create Earpiece.
Therefore you must conclude that if Aaron enters a box in timeline A, there are two Aarons in timeline B, whether or not Aaron A enters the box in timeline B.
If so considering, that Primer definitely entered the box between Tuesday and Thursday in timeline A, and Earpiece in timeline C, then in timeline D (the one where they both use the fail-safe) there should be six Aarons from 9-5 on Tuesday-Thursday (and three Abes): Primer (1), Primer B (2), Hooded (3), Earpiece (4), Earpiece B (5), and the final incarnation (6).
So, if they exist, where are these six Aarons?