Can only answer for myself, but I wouldn't have seen 60 as a date. For at least 2 reasons.
1. Since there is no list of what any of the abbreviations mean, (including for parts 1-3) how could a non-military layperson know that the 60 represented a date and not some other numerical military indicator? I would have read it as the number for the course, not a year.
2. Also, how many times on other projects over the years have we been told to key the full dates if present, rather than partial dates?
Having keyed a lot of the images for parts 1-3 of these records, I can tell you that I honestly didn't know that the "60" represented a year and not a course number, and never keyed it at all. Now I know.
Perhaps I'm wrong, but the keying images provided with the instructions for part 4 look like the ones that were used for part 3-so far I've not seen any images that I've downloaded look like the examples provided for part 4. Maybe just haven't got to that type of image yet.