Historically, the thinking has been that back-up is a one-man job: the pecking order was fluid, based more on form, and players such as Nick Evans, Stephen Donald, Colin Slade, Cruden and Luke McAlister would come and go.
That strategy wasn't overly successful. When the time came last year, the All Blacks didn't really have convincing options at first-five to step up after Carter's groin had been torn.
Such a scenario seems unlikely in 2015 and it's of more interest to ponder who of Cruden and Barrett will be the better player by then.
Nor should anyone dismiss the prospect that by 2015, while Carter may still be willing and able, that he might not be the first choice.
His performance in Brisbane last month was down on the benchmarks he sets himself and forced him into some serious self-examination.
The challenge he has set himself is to continue to be a better player and advance his place as one of the most outstanding No 10s the world has seen.
It's ambition on a massive scale but he needs the mental stimulation after 10 years and almost 100 tests. The way he played in Edinburgh suggests he's accepted the challenge - looked deep within and concluded he can achieve his goal.
That makes life tough for Cruden and Barrett. It leaves them forever compared with Carter, a once in a lifetime talent. But Cruden is used to that; he's not sucked into the trap of trying to be the same player and make the same impact.
"I just try to go out there and put my own spin on it," he says. "Obviously Dan has been the benchmark for a few years. But we are totally different players."
The second problem with Carter's likely continued involvement is that in all probability, it leaves Cruden and Barrett fighting their own pecking order battle to determine who is No 2 and who is No 3.
The indications are that, on this tour at least, Cruden remains the preferred back-up option. This is his third year with the test side and he won his 18th cap overnight.
"We always wanted to start Crudes [Cruden] and to keep developing him," revealed Hansen when quizzed about how much thought was given to starting Barrett at 10 against Italy ahead of Cruden. "The right place for Beauden was to come off the bench with his ability to cover first-five and fullback. He showed us last week that he is comfortable in the black jersey at 15."
It's debatable whether the pecking order between the two will look the same this time next year. Cruden's running game is top notch and he adds to the mix by being on the bench where, as he was against Australia in Brisbane, he can be thrust into the game to open up the defence, inject pace and width and stimulate the attack.
It's a more than handy option but at the same time, Cruden's performances against Argentina and South Africa when he started, lacked a touch of authority and composure.
Barrett has been gently exposed to the physical and mental demands of test football this year. He is only 21; there is time for him to develop the tactical and technical side of his craft and a belief that he may have a better all-round portfolio than Cruden.
Hansen and the selectors face a delicate task in giving both prodigies a fair go over the next 12-18 months and keeping them motivated; keeping them moving towards Carter and 2015. There will be tough calls to be made, disappointments to be countered and egos to be fixed. Hansen believes he can see a way to run with three first-fives and keep them all happy; keep them all believing.
