OK, final report.
It turns out that the SCB withdrawal slip includes a power of attorney (in Thai), so it can be used sort of like a check.
I had to send a trusted friend in Thailand a signed copy of my passport, signed withdrawal slips (I sent 3, which he had earlier sent me) and the ORIGINAL bank book. SCB branch also said they may verify by a Line video call.
Well sent all, my friend was a long time SCB customer known to the branch manager, so no Line call was needed. The account was brought to zero by paying him and he immediately wired the money to me.