Is this a case of selective reading?
Clause 5.24, addressing weld profile, states that all welds shall meet the visual criteria of Table 6.1 and shall be free from cracks, overlaps, and the unacceptable profile discontinuities exhibited in Figure 5.4, Table 5.9, and Table 5.10, except as otherwise allowed in 5.24.1, 5.24,2, and 5.24.3. Since there is no distinction between a tack weld and the final production weld, the criteria is equally applicable to the tack weld, each weld bead if making a multipass weld, as well as the final weld.
There are no provisions limiting the visual criteria to the final weld, quite the contrary, clause 6.5.2 states "The inspector shall, at suitable intervals, observe joint preparation, assembly practice, the welding techniques, and performance of each welder, welding operator, and tack welder to ensure that the applicable requirements of this code are meet."
I see no text that would allow a reasonable person to interpret the requirements of D1.1 to permit welding over cracked tack welds, slag inclusions, individual weld beads, or other weld defects and state the requirements of D1.1 are met if the final weld surface meets the criteria listed in Table 6.1. Clause 6.5.2 is in line with the credo that visual inspection must be performed "before, during, and after welding to be effective.
Best regards - Al