Robertson would not say Labour’s tax policy was a bottom line. He wouldn’t rule anything in or out. He declined to even use such language.
What he said repeatedly was that “a Labour Government” would implement that tax policy.
He did not specifically define what he meant by “a Labour Government” but it was understood to mean a majority Labour Government that did not have to negotiate with anyone else.
It was so well understood that National leader Judith Collins was able to reasonably claim that Robertson had not ruled out negotiating additions to tax policy in any coalition negotiations with the Greens.
A very perceptive article by Audrey Young.