The statement you have quoted has been deleted. The revision to Sec.47.a.i. says this: "A line must be left blank before the beginning and after the end of the entire labeled statement or formal proof." The newest errata/addenda to our lesson book is dated 2-22-2013 and is posted on the NFB's website. It applies to the original printing of the lesson manual. You can download it here: https://nfb.org/math-transcribing at the bottom of that web page.
We follow Braille Formats 2011 for the blank lines required before or after a page change indicator. There is also a helpful blank line summary in Appendix C of that document. Note that a Nemeth braille transcription has one exception to the rules when a spatial arrangement falls at the end of a print page.
Step-numbered items which we have reformatted as a list follow Braille Format rules for a list.
As more updates and errata are posted, it can be difficult to make sense of which rule to follow. If your lesson books have been revised beyond recognition, it might be a good idea to get a new copy and start over with the latest revisions.