I've had Comcast at 5 different apartments and only once did my IP address ever change while living at the same address, after a prolonged maintenance period when they ran new physical cables in my neighborhood.
The IPs are semi-static, and I would notice immediately if my IP changed since I have deny requests from any IP but my own to several webpages of mine.
Plus the IP address in the copyright infringement notice had a rdns hostname corresponding to an entirely different state.
I've got Qwest/CenturyLink and they change my IP quite frequently. A month ago they were changing it once a week. In the early evening (9-10 PM local time).
The IPs are semi-static, and I would notice immediately if my IP changed since I have deny requests from any IP but my own to several webpages of mine.
Plus the IP address in the copyright infringement notice had a rdns hostname corresponding to an entirely different state.