Also, I note that finding the answer to this on the academic calendar was pretty hard for me.

There are like four references to deferred standing, I list them in order of google search results (standing deferred “ubc academic calendar” course registration):

1. https://vancouver.calendar.ubc.ca/campus-wide-policies-and-regulations/grading-practices/standings (does not mention impact on registration)
2. https://vancouver.calendar.ubc.ca/campus-wide-policies-and-regulations/academic-assessment/deferred-and-supplemental-examinations (does not mention impact on registration)
3. https://vancouver.calendar.ubc.ca/faculties-colleges-and-schools/faculty-science/bachelor-science/illness-academic-concession-and-deferred-standing (has a hint, I guess? “Some science courses offered in Term 1 of Winter Session that are prerequisite to courses in Term 2 have scheduled deferred examinations in January. A student with Deferred standing in one of those courses is expected to write the January examination.”, which somewhat implies that you need to write the exam to keep the post-req)
4. https://vancouver.calendar.ubc.ca/faculties-colleges-and-schools/faculty-arts/bachelor-media-studies/academic-concession (about a specific degree in faculty of arts? has some lines that definitely could be misinterpreted to be about registration)

On the Science Academic Calendar registration page, it does mention that “prerequisites are courses that must be successfully completed before taking a course”, but without explicitly mentioning standings there’s no way I would find that without specifically worrying about this issue (which I probably wouldn’t, given that I’ve already been assured by my advisor).