A protest based upon alleged improprieties in a solicitation that are apparent before bid opening or the closing date for receipt of initial proposals shall be filed before bid opening or the closing date for receipt of initial proposals. For procurement by competitive sealed proposals, alleged improprieties that did not exist in the initial solicitation but which are subsequently incorporated in the solicitation shall be filed not later than the next closing date for receipt of proposals following the incorporation. In cases other than those covered in §A, protests shall be filed not later than 7 days after the basis for protest is known or should have been known, whichever is earlier. The term “filed” as used in §A or §B means receipt by the procurement officer. Protesters are cautioned that protests should be transmitted or delivered in the manner that shall assure earliest receipt. A protest received by the procurement officer after the time limits prescribed in §A or §B may not be considered.