Your citation applies specifically to Spanish. This is given on page 23 in Section 6.5f regarding the spacing of slashes in various languages. And this is why it is called the INTERIM manual. This rule was modified in 2005 to say that the slash would be spaced as in print for all languages, of course with some other exceptions having to do with pronunciation and other issues. This modification was not widely disseminated and so you and most other people just didn't know about it. This whole situation arose out of the special difficulties in formulating official BANA foreign language rules as part of the 1997 Braille Formats The Interim Manual is not a BANA publication, but it is based on BANA rules that existed at the time and it's all we have--UNTIL NOW. The new offical BANA Foreign Language Braille rules have been completed and the final document is being edited. The new rules clarify the slash usage--which is generally to follow print spacing. There are exceptions that have to do with unique issues in foreign language and other things and these are spelled out clearly.
In this case, if you have been following that slash rule for Spanish as given in the Interim Manual, you are correct. The usage I presented in the article is also correct. And when the new rules are published it will be much clearer for everyone and then you and I will know exactly what to do.
I hope this helps and I apologize for the complicated answer. The situation has indeed been complicated in foreign language and all I can tell you is that it is soon to be resolved at last.