I believe there was a small rock chip right at the bottom last year, it started off as about a 1/2" crack that hadn't grown at all. Until this week, not it's almost to the top. Add that to 2 other rock chips in that glass, guess I'll be searching for a new windshield soon.
Hot and cold from the defroster and snow on the outside will eventually lengthen even the smallest of cracks.
I just filled a couple of chips in my OEM windshield I picked up from road gravel over the previous winter. I used an over-the-counter repair kit (Rain-X) and a UV flashlight. Took about 10 minutes. Hopefully I've added a few years to glass. I do wish the epoxy was a little harder though. Rain-X was rated #3 on the Project Farm channel.