Subliminal messaging is quite interesting. As I recall, the talk at the time in 75 was about "ask yourself is you want to leave and if the answer is Yes, then go and vote to leave". Whereas the question actually really means "Ask yourself if you want to leave and if you do, vote NO to leave".
In circumstances like this, the old and the visually impaired tend not to read too clearly. Also people with Dyslexia or borderline Dyslexia may have difficulty with the statement. Personally I've been developing a visual form of Tourettes over the last 4 or 5 years. I see the most incredible swear words on billboards, tv text etc only to look again and find perfectly normal text.
Which probably says a lot about my state of mind....
This is why Salmond was determined for the Scots Independence campaign to be Yes to leave. Because it then made it a positive campaign. Exactly why this has been worded the way it has. NO is always negative as it IS a negative term.
The difference here will be social media. Where people will learn that Voting NO is a Positive step in leaving. Governments are finding their little tricks harder and harder to pull as the population has direct access to wildly varying themes direct to a phone near you.....
Why my Mil did what she did is a mystery to me as she's no longer with us, but I do recall Mrs S saying that she'd said she just got all flustered and didn't read it properly.
I recall the SNP won a majority in Scotland at their second term because they literally trained the unaware and unsuspecting public on how to fill in the PR ballot papers to get a specific result. That year the hard left Scottish socialist party got much lower votes than before. This had never been done before. I'm guessing that this kind of action will be more frequent in the future.