I would bet that over half of the people reading this are using a crampon/boot combination that doesn't "fit".
Before you call, "bullshit", read on, then go check your own rig again.
What do I mean by "fit"? I mean ZERO movement between boot and crampon when latched and even more importantly when climbing.
If you can flex your crampons by holding your boot /crampon combo between your legs and pull up on the front points and have the crampon flex...they don't fit. If you can move the toe of your boot inside the front bail either before it is buckled in, after it is buckled in or the toe migrates inside the crampon off to the side once you are climbing, the crampon doesn't fit.
If you can move the connecting bar sideways while holding your boot and crampon combo, your crampon doesn't fit. If your crampon's heel section can be moved by pushing or pulling on the center bar, the crampon doesn't fit. It your replaceable front points have any flex in them left to right...you need to tighten the bolt that holds them to the crampon body. Not a fit issue..but you get the idea.
I own 5 pairs of boots from La Sportiva and Scarpa currently. And 6 pairs of technical crampons. The crampons are from Petzl, Black Diamond and Grivel. I mix and match heel pieces and toe bales on each brand to get the best fit possible. And still there are some crampon and boot combinations that imo I simply find unsuitable for technical climbing.
Petzl and Scarpa both claim in emails to me that the newest Phantom series of boots and the Dartwin and Dart combination is a "good combination with no issues". I've seen people who should know better claim a "perfect fit" between the same combo. I wear a size 45 boot and mine simply don't "fit".
I own those same boot and crampons and won't use the combinations myself because of the terrible boot to crampon interface. And I really like both the boots and the crampons.
Black Diamond knows there are issues with many of the newer super low profile boot soles and smaller boots in particular. None of the crampon manufactures have any control over what the boot manufactures come up with. But they must modify their crampons to fit. Easier said than done from my own experience. BD is currently working on a new bail design to better the fit on all the new boots.
Having a crampon that doesn't fit perfectly just makes the climbing harder. It makes the climbing less safe. Dropping a crampon can literally be a life or death issue. It is never a good thing.
Some where between now (2011) and then (1980) we have allowed the manufactures to produce and we keep buying, some really bad combos for crampon and boot interface.
Why do I care? Having a "proper" crampon fit makes climbing so much easier. The crampons simply work better on hard technical terrain, especially so on ice.
Do me a favor and let me know if your crampons actually "fit" or don't. The reason I ask? I was playing with my Spantik's last night and the crampons I prefer to use on them. You can guess what I found...but my thought was, "sacrebleu, these don't fit!". And now you know how I came up with 50%.