Pretty sure, while there are ways of accruing objective evidence of SA shortly after it happens, most victims won't come forward before that time period, or they feel it's a complete violation of their space. Fair in both cases. These cases are typically argued by drawing a picture of the relationship between defendant/victim, building a character of both people, et cetera.
Could totally see him getting off without any charges if taken to court. You can probably imagine his lawyer's strategy in defending him.