I wouldn't be surprised if there's a correlation between the number of countries you've visited, as well as if you've visited specific countries and the wait time for interview. I've been waiting 71 days, but I've also visited 20+ countries and lived in three. There is probably a process for checking with the officials in those countries before clearing an applicant.

I'd also expect anything at all on your record to impact- like, for example, simply being stopped for questioning at the border, even if nothing came of it. Each event probably has to be examined by the agent assigned your file.

All theory, but It would make me glad frankly that they're thorough... makes the Nexus lane at the airport that much quicker..