No, though the current one started as a one shot, and ended up becoming a series. Still not quite sure how that happened.
Yes! It can be very difficult. That's why I have an Excel spreadsheet for the larger series to keep track of dates and when individual stories in the series are set. And even then, I often have to go back to refresh my memory on some detail I can't quite remember. I try very hard to maintain continuity. I also use the series spreadsheet to jot down stuff I know happened, that hasn't actually been in a story, but might be referenced at some point.