Why can I go for over two weeks and not have any issues?
My thoughts - take them as you will.
I'm still a noob at this whole UAV piloting thing, but I've been what most industries call a "safety officer" in the past, training people how not to die when dealing with equipment in my industry that can easily kill them. I tend to take conservative approaches to safety.
I follow a "prove this is safe" rather than a "prove it's not safe" internal guideline. Which means that even though I don't have the answer to your question, the fact that I don't have the answer to the root of your question (*can* I go for 2 weeks and not have issues, guaranteed) means I'm going to play it conservatively and assume my almanac needs a cold-start any time the GPS has been off for more than a day.
When I was training people on safety in my industry, and telling them not to do something for safety's sake, I'd often get the question "but at my last job we did it that way and never had a problem." I had several examples (complete with unpleasant video) of people who did what they wanted to do and got killed, or permanently disfigured and disabled by doing it.
But I would also tell them about the Challenger shuttle disaster. NASA knew the booster's O-rings were getting burned through by combustion gasses. They knew the problem got worse as the temperature got low. But they took the fact that they had flown 24 times before without killing anyone as evidence that the shuttle was safe, rather than just as evidence that they got lucky and got away with flying a dangerous vehicle.
They took a "prove it's not safe" approach to flight safety when they should have demanded proof that it was. And the result was that they killed 7 people, cost themselves (and therefore us) over 3 billion dollars, and did severe damage to their reputation and the US space program, the effects of which we're still feeling today.