I think some of you have missed the point I am trying to make.
In the "old" system, I went to the airline counter, with whatever was appropriate, ticket or otherwise, and got given a boarding card. There was no way that the same boarding card got issued twice.
Now, I can print my boarding card at home, on my PC, and if I want to, I can make as many copies as I like. If someone else who is not the person named used "my" boarding card, they would have been airside, no problem, and if I then turn up a few minutes later, and the system says, they're already airside, I then produce appropriate evidence that I am the named passenger etc, and I should get access airside. In the meantime, what, if anything, is done to trace the "duplicate" that went through ahead of me, and who has now done whatever they wanted to to get "lost".
I used to work airside, and I can think of a number of ways that I could get out on to the ramp having got airside, and once on the ramp, the possibilities are endless. I am not about to post them here, suffice to say that the new on linecheck in system has some serious security holes that has very little to do with the ID as such, and everything to do with the removal from the loop of the airline computer and checking that only one person has the boarding card. That's the point I am trying to make, that more than one person can very easily get access to a boarding card, not that the ID check is the be all and end all of that process.