There are lots of ways to talk about a "different past" in English. You can use the "difficult-to-remember-how-to-say-it-right" third conditional, (which English teachers love to teach students, because they know it and their students don't), but there are lots of other easier phrases and ways to indicate a hypothetical past
It was supposed to sail for 3,600 miles from the UK across the Atlantic to America. The plan was for it to become the first ever model, solar-powered boat to make a transatlantic crossing. However, things didn't quite go to plan when the four-foot long, 10kg vessel crashed after just six miles!
All things being equal, the unmanned craft should have left the South coast of England, sailed south to The Azores to catch some favourable winds and then it would literally have been plain sailing to the Bahamas and finally on to the USA. The whole journey ought to have taken six months months, but it turned out that it was only six hours.
All very embarrassing for Robin Lovelock, the retired NATO scientist who had spent 4 years designing the Snoopy Sloop. However, he wasn't too downhearted and was quite upbeat considering the circumstances: "There were always going to be problems, so I'm not too upset. If we had launched her a few miles further down the coast or an hour earlier, she would have missed The Needles (the place where the boat crashed - see picture) and would have been well on her way by now."
PAST CONDITIONAL - a different past
Could have / Would have / Should have
Could have = It was possible (to be different)
Would have = Imagining how it was possible (to be different)
Should have = It was the correct/right/best thing to do at the time (to be a different past)
These three options are all followed by a past participle (see below)
It could have been so different....
Maybe it would have been better to have waited for some calmer conditions, rather than the bad weather that the UK has recently experienced.
Perhaps they could have set sail from the west coast of Ireland, so that there wouldn't have been any obstacles on the way to the USA.
Or maybe they should have spent more time in the design process. After all, it can't have been built properly if it all went so wrong so quickly.