[SPOILERS]
This credit screen also still bugs me. As well as the "clock" hint on D3 and the actual clock in the lobby itself.
Actually, you have to use the computer with the C twice, as the hidden sequence tells you.
First: to even start the input sequence, when no other computer is accessible (even though the C is not yet displayed, it is the same computer)
Second: as the last input of the sequence
Once you relize, the sequence needs the C two times and you can only enter "y" in every computer once, after the very first input, this is actually a very logical solution.