i prefer the "whatever happened happened" version of time travel. so i would like to think that if anyone successfully went back 500 years in time and did well, we would have heard about it. the fact that we haven't heard about someone coming in from the future to change the world means that anyone who would have tried either died immediately because of landing somewhere inhospitable, was killed quickly as a heretic before getting a chance to do anything, or went on to live a completely unremarkable life that wouldn't get recorded in the history books, only it's in the past so everything sucks. also, with a random location, language is near guaranteed to be an issue
500 years in the future, it is more likely that time travel has become more commonplace. it is possible that people popping in from the past/future in random locations is a semi-regular occurrence, which could mean they'd have developed a technology to detect and save people that pop in in the middle of the ocean which, face it, would be the most likely location you'd appear in, given that around 70 percent of the earths surface is ocean
i like my chances a lot better in the future