Query about pf computation

Dear Respected Sir,

      Supposed Mr. X is working in a charitable institution from last 45 years that was exempted from epf.

   Now from April,​ 2015 this EPF ACT is applicable on all the institution.

   Now my query is as follows:

1. Institution have to deposit epf amount of Mr x from which date? Date of joining or from April, 2015.

2. If date of joining is not available than what date we can assume?

With Regards

Dayanand jha