Not a skater, but I have the idea (correct me if I'm wrong) that boot problems come in two main varieties:
1. something in the boot creates too much pain for the skater to perform to the best of their abilities.
2. something in the boot interferes with fine-tuned muscle memory so that a skater can't perform certain elements they previously could.
Brian Boitano talked about this in a coffee table book he put out years ago. He was talking about skates and said one time after he started wearing new skates he couldn't land the 3 axel. After finding no flaw with his technique he compared the old skates to the new and discovered that the heel on the new skates were 1/4 inch higher.
He also said that he sent his skates via Fed Ex to get them sharpened, so he obviously had more than one pair.
So if he had two pairs of skates and didn't just train one discipline while he was waiting for a sharpening, he likely had FOUR pairs of skates. Of course-if he did this at the elite level, he skated during the hey-day of sponsorship. As an unknown that would be very expensive, even for skating.
It does seem uncommon for skaters to have multiple pairs- because when they lose their luggage the first response is never "FedEx the backup!" At World's the few times I can recall it happening skaters have had their new pair (for next season) sent- but they aren't broken in. If it happened early season, I'd think they were SOL.
I've been wearing Graf Edmonton Specials for almost 15 years and they aren't all the same. I'm actually in a half size smaller than I used to be. The last pair I had that I actually trained in never really felt right. They had to get popped out a bunch of times but were never super comfortable. The last pair I bought felt like heaven right away. I've never had any issues breaking in those skates. Within a couple of hours of skating they felt good. Blade mounting is a whole other story
"Beautiful things don't ask for attention." -The Secret Life of Walter Mitty
Michelle had horrible boot problems in 1997 with her Ridell endorsement deal. It's talked about at length in Christine Brennen's Second book about the 98 Olympics (I can never remember the names of those books, even though I own them) and I saw them first hand over that 1996-1997 summer. They managed to work them out (I can't remember how either finished the contract and went back to her original brand, ended the contract early, or just used other boots-(t has been years since I read the book). It's pretty serious. When I saw Michelle day after day she was missing lutzes and flips and Danny Kwan would complain about her boots all the time.
Have we mentioned Mark Ladwig losing the heel of a his boot at 4cc in 2011? Not a boot problem over time, but how random.
As a teenager, my biggest boot problem was outgrowing them every 6 months.