Hello and thank you for your question.
It sounds like things are being done correctly. Income should be reported on the Schedule K-1 according to the trusts' tax year, which I assume is a fiscal year ending August 31st based on your question.
The CPA is correct in that the trust should not file a final tax return until all assets have be distributed to the beneficiaries. Waiting until after a trust's fiscal year end to do this would generally require the filing of an additional tax return and thus lead to more administrative fees. It is not in your interest to wait unless you reasonably believe there are more liabilities out there (if so, try to find them and get them paid prior to the fiscal year end). Your CPA should account for his fee on the final return also and I assume he/she will handle that part properly.
If all goes well you will be able to wrap up the trust and file the final return this year. I hope this is helpful.