(a) Whenever the purchaser of any tax lien on any real estate sold at a tax sale, his heirs or assigns, shall have obtained a deed for such real estate from the deputy commissioner or from a commissioner appointed to make the deed, he or they shall thereby acquire all such right, title and interest, in and to the real estate, as was, at the time of the execution and delivery of the deed, vested in or held by any person who was entitled to redeem, unless such person is one who, being required by law to have his interest separately assessed and taxed, has done so and has paid all the taxes due thereon, or unless the rights of such person are expressly saved by the provisions of section forty-nine of this article or section two, three, four or six, article four of this chapter. The tax deed shall be conclusive evidence of the acquisition of such title. If the property was sold for nonpayment of taxes, the title so acquired shall relate back to the first day of July of the year in which the taxes, for nonpayment of which the real estate was sold, were assessed. If the property was sold for nonentry pursuant to section thirteen of this article, or escheated to the state, or is waste and unappropriated property, the title shall relate back to the date of sale.