The events of 15 June 1991 are supposed to take place on a Sunday when in fact that day was a Saturday. All subsequent weekdays are also off, e.g. 16 June 1991 is a school day when in fact it was a Sunday.
Lea is repeatedly stated as being 17. Since she was supposed to have been born in October 2004 that would have made her 16 in June 2021 when the series is set.