That's part of the challenge.
If you're able to do an open-source check on the information that you receive, then you might be able to identify the IP range for a particular provider.
Now, as I alleged earlier—I think it may have been on Tuesday—it's possible that there are resellers of IP ranges. A large company may resell a certain range of IPs to a smaller company, and so forth and so on, until an address is sold to the subscriber. Just because the allotment of IP addresses was to a larger company, it doesn't mean that they're actually going to have the subscriber information that would be associated with that particular IP address at a particular time.
Police have the challenge of trying to identify which company might have provided direct services to whoever used that particular IP address.