When I talk about the Creatures of Yes being set in 1979, I don't' mean exactly 1979. I'm not trying to adopt all the exact fashions of that specific year. I think of 1979 as more of a stoping place; a somewhat arbitrary number that seemed (technologically and stylistically) a good place to stop. Because 1979 isn't just that year, it encompasses every year that came before it.
I was recently doing a puppet show at an elementary school upstate. The auditorium / gymnasium was straight out of the 1950s (maybe earlier). Nothing had been changed. It was a perfectly functional time capsule! They made announcements (the lunch menu, a weather report, the pledge of allegiance and the joke of the day) over an intercom from that era and it was delightful. If I was experiencing this sort of time travel in 2016, imagine what points they were still hitting in 1979 - probably back to the 1800s! Of course, we can still see the 1800s and even further back today, in a museum, but I'm talking about accidentally stumbling upon another time, by magic!
This sort of time travel magic doesn't always have to be accidental though, if you know what you're doing you can conjure it. The difference between an exhibit of the past and time travel magic is that the real stuff has life and is functional still.