those analyses were based on the announced policy that article 50 would be triggered immediatelyThen they were naive analyses rather than expert analyses weren't they?
Did anyone seriously think Cameron would stay on to implement Brexit? Only someone utterly clueless about British politics could have thought that - it was obvious there'd be a leadership change in the event of a leave vote.
It is also obvious that Article 50 was deliberately botched, the guy who wrote it have said so explicitly. 2 years is a stupid choice for the amount of time available, designed specifically to discourage people from trying to leave. So assuming it'd be invoked immediately anyway was a very bad assumption.
No matter how you slice it, the so-called "experts" were completely wrong and excuses don't cut it.