This is a good question. Many people have trouble with this.
Format Guidelines 2011 4.3.8 is a good reference, even though it specifically addresses headings, this is the correct way to handle the situation in any Literary code transcription, regardless of the print placement .
You commented that Formats 4.3.8 does not refer to number-letter situations. In actuality it does not specify whether the number or the letter comes first. IT works either way: letter-number or number-letter.
“Use the period, rather than the decimal point, [u]when a period appears between a letter and a number[/u].”
EBAE does not specifically address the print dot between numbers and letters. The section on reference numbers does not have any examples for this either.
The best example in EBAE is found in section VI.27.d Abbreviations Example: S.W.1
There is a very nice explanation in The Lesson Manual 2009 17.5a Section numbers and reference citations.
"… Print dots used as separators in such citations should be represented by the braille decimal point [u]only[/u] when they occur between arabic numbers. When a dot occurs[u] [/u]between roman numerals and Arabic numbers or [u]between[/u][u] numbers and letters it should be represented by the braille period[/u]. Example: LA.E.2.4.1
Other references I like to use when I can’t find anything that specifically refers to the issue at hand, is the brailled version of EBAE and The Lesson Manual. In this case, the section numbers in both manuals have a print dot between numbers and letters. It’s easy to see how it’s been brailled in an official reference book.
Hope this clears things up for you.