When I build winter tyres I plan for them to roll for thousands and thousands of kilometres... the one flat I did have was on a tyre that had seen well over 10,000 km and the culprit was a screw that had backed itself out a little and had worn through the liner and the tube. I am not sure how long it took to do this but the liner was thicker and probably saved me from what would have been a more immediate flat.
My current set of winter tyres is going into their third season and using averages, they have already seen nearly 10,000 km... when I pulled the winter bike out of storage and topped up the tyres they were still in the rideable range of pressure and that was after being stored over 6 months.
Will be building another set here soon for my other winter bike as it lent it's tyres to my daily driver while it gets used for general riding but is primarily my shopping bike / pickup truck in the winter and is very stable even without studs on it's 2.3 Kendas.
I have several tyres already made up and still have tyres I built 5 years ago that could serve me well but I want to stud those 2.3's as in themselves they are an excellent winter tyre with a great tread pattern and very important is that they are also rather supple in cold temperatures.
This can make a huge difference as some bicycle tyres become very stiff and inflexible in the winter and this really reduces ride quality and traction.