Exactly.
Star Wars Land opened on May 31st, 2019. But on May 28th-30th they had a series of invited previews and premiere parties that the public wasn't invited to. They had the big celebrity opening ceremony and party on May 30th.
Cars Land opened on June 15th, 2012. But in the days leading up to June 15th they had invited previews and a big splashy premiere party on June 14th that the public wasn't invited to.
I get a real kick out of
@Darkbeer1 and his passion for this topic. Like most Disneyland fans, I had been using July 17th as the "opening date" for Disneyland for many years. Through the archival material and clear evidence Darkbeer provides, it's now obvious that for at least the first 10 years Walt and his team at Disneyland considered July 18th to be "opening day".
A fun quirk of history how it changed and how Disney itself reclaimed July 17th as the opening. If I were to guess, the change would have traced back to the anniversary TV specials in the 1980's where the celebrity hosts would talk wistfully of the disaster of opening day, ladies heels sinking into the wet pavement, etc.
But before then, the mess on July 17th would have been fresh and embarrassing memories for Walt and his team in the 1960's, so the accurate date of July 18th was used and July 17th was conveniently forgotten.