The extended Ireland squad for the World Cup could stretch to between 40 and 50 names when it is announced in the coming days.
Joe Schmidt will have already identified those with claims for Japan.
There is the case of who will go - and there is the question of who will make an impact?
Ireland Caps: 3, debut v Italy, February 24, 2019.
It is not just Ross Byrne who has to worry about the Connacht out-half.
The real advantage to playing in the Western Province is that patience is a necessity, not an option.
The rapidly maturing Roscommon man has been able to work through his goal-kicking woes and defensive deficiencies.
This has been a season's best in terms of the 26-year-old's kicking, game management and leadership.
Carty impressed Schmidt enough to earn three quickfire Ireland caps in the Six Nations, including 22 minutes against France.
It remains to be seen whether Schmidt sees Carty as second choice or a straight third choice behind Jonathan Sexton and Joey Carbery.
Certainly, the place of Carbery as the natural number two is not cut and dried.
Ireland Caps: 7, debut v Argentina, June 6, 2014
The retirement of Rory Best at the end of the World Cup will leave the door wide open for Herring to nail down his position as Ulster's starter.
Above that, the 29-year-old South African-born hooker is in line to travel to Japan as Best's back-up.
Quite simply, Niall Scannell has not been able to convince in his role as Munster's frontliner.
The problems with Sean Cronin have been well-documented, the hooker rated more highly by Leinster than by his country.
The throwing inaccuracy that caused the Limerick man's downgrade in the Six Nations leaves the number 16 shirt wide open to interpretation.
This is one position in which there will be an almighty battle between Cronin, Scannell and Herring to make the three seats for hookers on the plane and, thereafter, the bench in behind Best.
Ireland Caps: 0
On the face of it, Ireland are well-stocked for second rows, with Devin Toner's medial ligament injury costing 4-6 weeks instead of Japan-ending serious surgery.
The Leinster lineout caller, James Ryan and Iain Henderson are automatic choices for Schmidt.
In addition, the repatriated Tadhg Beirne, the rejuvenated Ultan Dillane and under-rated Quinn Roux make compelling cases.
However, Kleyn will be Ireland qualified on the eve of the World Cup and the marauding lock has a point of difference.
The hulking 6'8" tight-head scrummager weights in somewhere north of 120kilos.
However, no one really knows in advance how effective he can be at international rugby.
The list is long of players, who look the part until they fall apart under the weight of pressure.
Kleyn arrived in Munster on August 8th in 2016, meaning he will qualify two days before Ireland's first pre-World Cup friendly against Italy on August 10th.