Each and every one had a common denominator. None of them managed to go from start to finish without losing. Put another way, no team over the last 14 years has stayed unbeaten throughout the six pool matches and gone on to lift the trophy.
After what Leinster did to Bath in Dublin on Saturday night when they achieved the distinction of being the first Irish team to put 50 points on an English club in Europe, nobody will be one bit surprised should the defending champions become the first.
Only they and their ancient provincial rivals from the same RaboDirect PRO12 competition, Munster, have completed the first four rounds of the current Heineken campaign without losing and only Munster can boast a 100per cent record
Cardiff Blues' stumble against Edinburgh in Murrayfield and Toulouse's failure to cope with the mightily irresistible Harlequins in France on Sunday afternoon has left the Irish superpowers leading the charge towards the quarter-finals.
Leinster, away to Glasgow and home to Montpellier in the New Year, ought to qualify in a style which brings them the luxurious reward of remaining in Dublin all the way to the final at Twickenham next May.
Older Leinster hands like Brian O'Driscoll will be wary of such a scenario lest history repeats itself.
Nine seasons back, under Matt Williams, they won all six pool matches, saw Biarritz off in the quarter-finals at Lansdowne Road and went back there for the semi a few weeks later only to be undone by the unfancied Catalans from Perpignan in their bacon-and-egg strip.
The consequent all-French final in Dublin had an underwhelming effect on the Fair City.
Breezing through the pool competition and arriving undefeated for the quarter-finals stage has never failed to end in the most anti-climactic of knock-outs for those concerned. Leicester under Dean Richards' on-field command were the first to suffer such a fate, winning all eight matches en route to the 1997 final at Cardiff Arms Park where Brive gave them a severe four-try runaround.
Wasps went the same way at the hands of the French holders the following season, winning their six pool matches only to be given the heave-ho by Brive at Loftus Road in the quarters.
Three seasons later Bath, with a young Mike Tindall and a still younger Olly Barkley, won six-out-of-six before they ran into Llanelli in the last eight at The Rec and ended up being wrecked to the tune of 27-10.
Not even Leicester in their pomp could stay unbeaten throughout a European campaign. Going for a hat-trick of titles in 2003 under Martin Johnson and a platoon of other England World Cup winners, they cruised through the pool without losing to earn a quarter-final against Munster at Welford Road.
A fat lot of good it did them, Munster winning at a canter, 20-7, in getting some of their own back for losing the final the previous year when Neil Back infamously slapped the ball out of Peter Stringer's hand before he could feed a late Munster scrum in front of the Tigers' posts.
Two seasons after their shocker against Perpignan, Leinster suffered an overpowering sense of déjà vu.
Again they won all six pool matches and again they were counted out at Lansdowne Road, this time by Leicester in the quarters.
The following season, Ireland's capital province went to Toulouse at a time when it seemed as if nothing could stop the holders retaining their title as unbeaten qualifiers. One of the all-time epics ended with Leinster storming through 41-35 in a classic of almost a point-a-minute magnitude.
Since then three more clubs have scooped the pool in the pre-knock-out stage and still come up short.
Biarritz lost to Northampton in a home quarter-final in 2007, Cardiff Blues to Leicester on the cruelty of a penalty shoot-out at the end of their tied semi-final against Leicester at the Millennium Stadium and, most recently, Northampton, overwhelmed by Leinster's stupendous second-half in the same arena by the banks of the Taff last season.
They say there is a first time for everything in which event a strong case can be made for expecting the European crown to remain in Ireland, either with Leinster winning it for an unprecedented third time in four years or Munster making it three in six years.
After two semi-finals over the same period, what odds against an all-Ireland final in London on the third weekend of May?
Both provinces are on course for home ties in the last eight. At least one other RaboDirect team, Cardiff Blues or Edinburgh, ought to join them from Pool 2.
London Irish, their prospects badly damaged by last weekend's home loss to Racing Metro, still have a decisive role to play, what with the Blues at home and Edinburgh at Murrayfield.
Ulster, two points clear at the top of Pool 3 after taking ten out of ten against Aironi, now come to the hard bit. Leicester are next up, their New Year trip to Ravenhill bound to evoke memories of the one they made there on a Sunday lunchtime eight years ago when Ulster thrashed them 33-0 only to suffer a bigger thrashing, 49-7, in Tigerville the following week.
The danger for Ulster, and Leicester, is of Clermont Auvergne coming from behind and finishing first past the post. The Michelin Men will expect maximum points from Aironi in Italy before returning home in the last pool round for what will probably be a winner-take-all decider against Ulster.
Pool five, is Saracens' to lose after their double over the Ospreys and Quins' magnificent victory in Toulouse makes it an intriguing Anglo-French duel in pool six.
Whoever finishes second is still likely to qualify as one of the two pool runners-up with the best records.
The Scarlets will almost certainly be the other provided they recover from their double set-back against Munster and win their remaining ties at home to Northampton and away to Castres.
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