You can twist the story back and forth, say the dates are not relevant, etc.
The 3-pilot crew operation of SIA was flawed from day one. Make no mistake that I have a very comprehensive understanding of how it was conducted. In this regard I also have very good understanding of the ICAO safety requirements and how SIA goofed in reflecting them in their FAM (even though my spelling and grammer sucks).
The Captain going to the toilet is not an issue at all. Now you are giving yourself selective memory when it comes into the dark silent don't tell operations of SIA leaked by a whistleblower.
If you are real, and I presume you are, you know very well how the 3-pilot crew operations were conducted. At every fleet meeting the issue came up over and over again with the same result. One big grey area (intended to be so).
On line 99% of the time the captain of the 3-pilot operation ended in the bunkroom sleeping (without proper oxygen equipment), leaving two improperly licensed and trained first officers at the controls.
I suppose the next thing you want to say is that this never happened (then you will sound like SIA's lawyers).
Proper 3-pilot operations as intended by the design of the B747-400 (the crew bunk oxygen system) would assume that the relief first officer occupying the left hand seat is, a) properly licensed (regulatory requirement), and b) left seat trained (safety requirement).
Outside these parameters the left hand seat can be unattended for a period of time necessary for physiological needs (toilet) only.
SIA and your understanding is/was that if the Captain can go to the toilet and leave his duty station unoccupied, why can't he be gone for 3.5 hrs sleep in the bunkroom. Ken T of CAAS in front of an FAA representative tried to defend CAAS and SIA by saying that the Captain can be gone for 3.5 hrs (sleep in the bunkroom), since sleep is a physiological need. That would be OK if you leave a qualified crewmember in the left hand seat duty station (a first officer without left hand seat training and certainly without an ATPL does not qualify).
We can argue about this all day. One thing remains fact, CAAS did cover their backside and informed SIA that this practice is no longer allowed as well as finally taking the ATPL issue seriously (in a different notice).
Of course none of this would have happened, if this matter was not brought to the attention of ICAO, FAA and NTSB. SQ006 doesn't help as it had/has the potential to become a legal mine field.
May I suggest you read SIA's FAM (Flight operations Manual) previous to SQ006 with full attention in regards to 3-pilot crew operations and realize the flaws and inadequate attention to the ultimate goal, safety.
If you need the page numbers, let me know.
As for SQ006 cause of the accident discussion, etc, yes the swiss cheese is real and TPE airport markings may be one of the slices. However many flight crews that day looked out of the window of their hotel room and decided not to go.