I am sorry to say that I don't have a good answer for this one. Both deletions and actual bracketed texts should be transcribed in brackets following the BTP instructions. If we update the instructions at some point, this is probably something we would change due to the potential confusion this markup creates. However, as you can imagine, that would introduce its own issues with consistency, retraining volunteers etc. and therefore isn't in the cards anytime soon. So for now, please follow the instructions.
Will do. Thanks