If a box appears in the midst of line-numbered text, but is not itself line-numbered, can it use line 25? I believe it can, but I wanted to be sure. (For the record I am maintaining the 2-cell margin on the R with the box lines and the boxed material – just in case you were curious.) 🙂
I agree with your suggestion that these two types of material (boxes and stage directions) which are NOT line numbered but appear WITHIN line numbered text CAN use line 25. See BF 15.3.1.