So teams can use, for example, seven batsmen while batting, then use all their specialist bowlers and put batsmen on the bench in a 12 or 13-a-side system. Official? No.
Compare New Zealand's buildup with that of the last time the cup was staged in this part of the world, in 1992.
Then, New Zealand were well beaten by England 3-0 immediately before the tournament. Only one half-century was scored, 52 by Ken Rutherford in the second game at Dunedin.
They lost by seven wickets, with 97 balls not required by England at Eden Park, by three wickets at Carisbrook and by 71 runs in Christchurch.
Yet consider what followed: a tournament-shaping win over Australia on a sunny Eden Park in the opening match, followed by six successive wins, before a round robin loss to Pakistan, then the crushing semifinal loss to the same opponents.
This time, New Zealand have won six of eight leadup games against Sri Lanka and Pakistan, against two defeats.
Coach Mike Hesson has professed his delight that his squad has primed itself ideally.
Is there a right and wrong preparation? It's hard to argue that stringing wins together must help the confidence, and imbue players with the knowledge that they are on track to, at the least, be competitive when it counts.
On the other hand, the 1992 experience suggests it's more about getting it right when it matters and don't get overwrought if the preparation is skew-whiff.
There's also the different mentalities of players from around the world, Pakistan being the perfect example.
In 1992, they were a rabble through the first half of the round robin. Had rain not stopped England, after they'd rolled Pakistan for 74 in Adelaide, they would have lost four of their first five games and effectively been gone.
Then they had three wins in seven days - Australia and Sri Lanka in Perth, then New Zealand in Christchurch - and Imran Khan's cornered tigers became unstoppable.
Whatever the odds to win the cup, that's why Pakistan would be a team everyone will want to avoid in a clutch knockout this time.
They don't have anything like the quality of players they did 23 years ago, but they can dig deep and seize a moment as well as any team.
And that's what the cup is all about - recognising an opportunity and grabbing it.