Those are documented, but not necessarily in the paper. You can find the info at clinicaltrials.gov. Check out this current trial for breast cancer treatment by Merck Sharp & Dohme LLC for example. For the control arm, they are allowing doctors choice from a set of alternatives. Assuming the doctors are selecting control treatments to improve chance of survival, this test is comparing the new treatment to "the best known treatment for this specific cancer".

https://clinicaltrials.gov/study/NCT07060807#study-plan