[Imampaictjg]

After some further pondering and upon rereading the wording " the left and right forearms in the case of other Kamae" this is still troubling to me. But I think the intent is that the hands are valid if they are being used in the case of other kamae...

Does the Japanese version help? Maybe a native speaker or Kanji savvy individual can get more out of it. To me it states that essentially left as well as right are valid with other non-chudan kamae, but I am probably reading my own perception into it...
小手部は、中段の構えの右小手（左手前の左小手）および中段以外の構えなどのときの左小手また は右小手。