HPV, mainly HPV-16 is in the oropharyngeal, has different biology than HNSCC usually caused by tobacco and alcohol. As such, HPV has better response to treatment, and prognosis, but most prior studies, statistics do not include this fact, and just bundle all HNSCC, oropharyngeal cancers wether HPV or not, together, but will separate them in the future. I heard of up to 50 percent improved overall response rate, so each stage is different. There are other factors involved in recurrences, mainly the tumor size, it's location, nodal involvement, extracapsular extension, and other factors, and unfortionatly do happen, but everyone is different.

Good luck with the rest of the treatment, and recovery, and it's a good sign if the doctors are happy.