Yeah you're more or less correct. The list of differences between traditional and simplified is about 1 page long and appended to the end of dictionaries. Most people don't bother to actually look at it but you just kinda pick up most of them eventually. Like I don't think most people are gonna recognize "hiccough" or "phial" or "furore" without context clues but "colour" isn't going to give anyone trouble.

By random places I meant like one time I bought a notebook that was made in the mainland in the 2000s and all the appendices were in traditional for no particular reason. Or sometimes people will still use the traditional character for things and not even notice. I could've sworn that was when I was a kid and was being taught to read in simplified I was taught 魚 and not 鱼 for example.