Query on Validity of Sale Deed

I am considering buying a property. This property is a plot in a layout carved out of a survey (let us say Survey X). The survey originally belonged to Persons A, B, C. Persons A, B, C executed a registered General Power of Attorney on behalf of person D. The GPA states that D is authorized to "generally do all such acts, deeds and things in respect of the schedule property", etc. and mentions Survey X in the schedule property. Person D later executed a registered General Power of Attorney, sub-delegating to Persons E, F, G. The GPA mentions Survey X in the schedule property. The document mentions that the earlier GPA empowered D to sub-delegate all powers in favor of third party. The absolute sale deed states that A, B, C are vendors represented by GPA holders E, F, G and selling the plot to Person H. The document is signed by E, F, G and H. It is not signed by A, B, C, D. All the above transactions /deeds happened before 2011 Supreme court rule stating that GPA is not valid for selling property. Now, I am planning to purchase the plot from H. Is it safe to buy this property, as there has been a delegation of GPA in the chain?