An update on this.....
I called Line, and they asked me to take the skis in to an authorized dealer. I did that, and a couple of their techs took a look at the skis. They thought that the crack was likely impact damage, but there was no evidence of anything hard enough to crack an edge.
They took some photos and sent them off to Line. Line / K2's position was that if there was any sign at all of impact, it was impact damage and not covered by warranty. The shop offered to send them in if I wanted to push the issue, but I'd be on the hook for the shipping fees. I decided not to send them in given the decision the dealer got back. The dealer did offer to have me talk to their warranty contact directly to see if that would help as they want to keep customers happy.
I emailed the rep with a few more photos and a summary of the situation. I was honest, and said that I was certain there had been an impact, but it was in my view pretty minor, and I was surprised the edge cracked. The rep called me within a few minutes and offered up a coupon for 40% off if I wasn't happy. That was nice of her, but I still wasn't thrilled with the prospect of having to replace a newish pair of skis from a little hit. She offered to escalate to a warranty supervisor and would get right back to me.
I left things about a week, and followed up. No response. I tried to contact the rep every couple of days after that, but it took two more weeks to get a response to an email or phone call. I eventually got an email saying sorry, we're busy this time of year, it's impact damage, no warranty coverage.
I'm going to ski them and just use the damaged edge as an outside edge. The techs who looked at it thought it would be fine, and that I wouldn't even notice it.
I like the skis enough that I'll buy them again if and when these give out. Maybe I just got a bad set or maybe I hit something harder than I realize.
Skis - A
Durability - C
Initial customer service experience - A
Subsequent customer service communication - F
Warranty decision - B-
I'm fine with Line's decision not to replace them under warranty. I hit something, and the ski broke. It broke too easily in my opinion, but I respect that their policy is not to cover anything where an impact is evident. I would have given them an A instead of a B-, but the offer of a discount on a new set vanished somewhere during their 3 weeks of radio silence.