(a) The provisions of this article shall not apply to contracting services. However, purchases by a contractor of tangible personal property or taxable services for use or consumption in the providing of a contracting service shall be taxable beginning March 1, 1989, except as otherwise provided in this article.
(b) Transition rules. — The exemption from payment of tax on purchases of tangible personal property or taxable services directly used or consumed in the activity of contracting, as defined in section two of this article, which expires as of March 1, 1989, shall nevertheless remain in effect with respect to:
(1) Tangible personal property or taxable services purchased by a contractor on or after said first day of March in fulfillment of a written contract for contracting, as defined in section two of this article, that was executed and legally binding on the parties thereto on or before February 15, 1989; or in fulfillment of a written contract entered into after February 15 pursuant to a written bid for contracting that was made on or before February 15 that was binding on the contractor, but only to the extent that the bid is subsequently incorporated into a written contract; or