September, I think you'll have a job on your hands with that one regrettably, I suppose it depends on what your vet says in his notes
As Rachel points out, any treatment that the dog has received prior to insurance is generally excluded - it will have been endorsed on your policy. It wont just be Pinnacle, it will be a decision across the board with 99.9% of insurers.
With any endorsement you can query it at renewal, they may then make a decision to continue with it or take off the endorsement - however, I presume that you are claiming for another tummy problem so it is doubtful that they will - I would be careful with other insurers too.