this transporter room apparently has no 'twin' on the opposite side of the corridor
It should be pointed out that the idea of "mirroring" as such would still allow for another transporter room across the corridor - if we don't treat it as a set reuse, but as a true reversing of every single detail. That is, the putative other room would be the mirror image of the existing set in plan, and the back wall detail would be selected from among those set variants that would not necessarily protrude.
This would not provide us with an identity for a known set variant as such. However, it would provide just that by implication: the mirror image of a putative corresponding room on the opposite (port?) side of the ship would in that case be a double mirror, and would thus have the same plan as the existing set. So at least two slightly different transporter rooms would now plausibly exist simultaneously, in a ship that would remain laterally symmetric. (That is, if lateral symmetry is found desirable...)