Tax

It is mandatory to mention the notification number and details in the receipt issued by the donee. If the details are not available and it is not specifically mentioned that the donation is eligible for the deduction u/s 80G the donor may be denied the benefit.

if on the donation receipt it is not mentioned that it is subject to deduction

u/s 80G THEN IT WILL NOT BE ALLOWED AS DEDUCTION U/S 80G...

I thing if that Devastanam is registered for deduction of Tax u/s 80G then only it is allowed as deduction.

As far i believe it always mentioned in the receipt about the details of the notification and that it is deductible U/S 80G. If its not then they might not have registered for 80G. So you won't get any benifit if its not registered.