IT is a little late in the day for a post-mortem but there are still salutary lessons to be taken from Scotland's 21-15 loss to Tonga in Aberdeen two years ago.

It will always be remembered as the match that brought an end to Andy Robinson's period as Scotland coach. In its immediate aftermath, it was easy to highlight the fact that over the preceding 13 months Robinson had led the side to a first pool-stage exit from the World Cup and had then been in charge as they suffered their first Six Nations whitewash in eight years. In other words, the charge sheet against him was pretty damning by that point.

Yet any sensible analysis of Robinson's time in charge would also focus on the fact that he had been at the helm for two wins against Australia, had guided the team to a win against South Africa and had claimed the historic first of a Test series victory in the southern hemisphere when his side beat Argentina twice.

Nor was all this ancient history. Just a few months before his exit, Robinson had taken Scotland on a three-match unbeaten tour of Australia and the South Pacific. Only the previous weekend, they had put in a decent performance against South Africa, never humiliated over the course of a 21-10 loss at Murrayfield.

And yet the collective memory of Robinson is of a man who had run out of ideas, who had nothing left to give. In the caricature he looks haunted and dishevelled. On closer analysis, that picture is absurd but it should serve as a warning that things are rarely as bad as they are portrayed in the lean times but rarely as good as they are sometimes painted, too.

Which brings us to the current coach Vern Cotter. The New Zealander, like Robinson and Frank Hadden, has made a promising start to his Scotland coaching career but it is still just that: a start. His record to date is played six, won four, but the results have all followed the form book. The teams the Scots have beaten - the USA, Canada and Argentina twice - have all been below them in the world rankings. The sides they have lost to - South Africa and New Zealand - were both far higher up that scale.

In other words, while Cotter's Scots have won many admirers for their up-tempo, self-confident, energised style of play, they have not yet won a game they were expected to lose. Nor have they even played a game of any sort in the context of a genuine competition. To date, every match under Cotter has been a friendly.

Perhaps it would be better to call them rehearsals. In just over two months' time, the serious business will get under way as Scotland open their RBS 6 Nations campaign against France in Paris. The World Cup comes round in September. The team and the coach can only really be judged by what they do in those tournaments.

And yet, it is impossible to ignore the transformations there have been in some players. Greig Laidlaw looks sharp and spiky again, having shaken off that infuriating habit of crabbing sideways before releasing the ball. Ross Ford looks rejuvenated, no longer the one- paced and predictable basher he had become. And if you were looking for an easy time of it around the rucks, you would probably rather play against the Krays than the Grays right now.

If Scotland carry on where they left off against New Zealand, they should beat Tonga by a street. The trouble is, Scotland teams have toiled awfully in such circumstances in the past. Going back to the game in Aberdeen in 2012, it is difficult to say exactly where Scotland got it wrong but there was a powerful impression that they were unable to make running repairs when things started to go awry.

If Cotter has tightened the team up in any area, it should be that. The players themselves have spoken of the coach's demanding standards but also of the way he has kept things simple by laying down a few ground rules and trusting them to figure the rest out for themselves.

"Vern and all the other coaches give you the template," said the centre Alex Dunbar earlier this week. "But a lot of it is player led; I think that's the best way.

"It is the players out there who are doing the job at the weekend, so it has to come down to them. It has to be good for the team. The more the players can lead that and manage that, the better it is for the squad."

Given that Scots have generally been open to the idea of an outsider as a coach for about two decades, the wonder is that it took us so long to get round to appointing a New Zealander, when you consider the cultural ties and mutual understanding. More so than Matt Williams, Robinson or Scott Johnson, Cotter has suggested he knows what makes Scottish players tick. That he has allowed them to play as they see fit has been as heartening as any numbers on the Murrayfield scoreboards over the past two weekends.

Tonga are fierce and fearless opponents, skilful on the ball and devastating in the tackle. They are also a far better organised team now than they were at Pittodrie two years ago. The confidence Cotter has engendered in his players will evaporate if their concentration drops from the levels of their past two games. They have the game to win, but they will have to have the winning attitude as well.

It is too early yet to say that Scotland have turned a corner but with a victory in Ayrshire today they will certainly have a straight road in sight.