This and the fact that there does not necessarily need to be a specific rule in place in order for a punishment to be carried out, that is up to staff discretion and critical thinking as stated in the SCP-RP Staffing Guide:
"Please note, while the MOTD is meant to be all encompassing, it’s both impossible and impractical to cover every single situation that can occur. As such, some general rules may apply to many situations. For example, exploiting the surrender SWEP to be able to shoot without being seen to have a weapon is clearly an exploit. Use your critical thinking skills to use these general rules to apply them to situations you may be involved in, and feel free to ask a more senior staff member for help on discord if none are online. As a rule of thumb, if something feels wrong and gives another player an unfair RP advantage, it probably is wrong!"
Think of this except above as a sort of reverse Ninth Amendment. SMT is not omnipotent, they cannot predict every situation. D-Class are not supposed to be able to obtain an ethereal without the direct action OF an SMT member anyways, therefore SMT saw no reason to make this a general rule as, again, they are not all knowing and didn't expect a QM to abuse their job and give D-Class ethereals.