I know that YC has a standard RSPA... but I'm also fairly certain that their template is not used universally by all YC companies (eg. Quora, who probably already had other RSPA docs [1]). Therefore, the standard YC RSPA cannot probably be deemed binding after the fact. (IANAL)

[1] http://techcrunch.com/2014/05/11/quora-y-combinator/