If the Senate moves ahead with the trial without receiving the articles, I'm wondering if that will give any witnesses subpoenaed a legal angle to refuse the subpoenas on the grounds the Senate trial is not legitimate?

I've wondered all along if this might be Pelosi's real game at hand here, not that she's trying to influence the Senate's handling of the trial. They are protecting themselves against the Senate calling witnesses the Democrats don't want to testify. Biden's already said he will refuse any subpoenas. By withholding the articles, Pelosi is creating a legal justification for any unwilling witnesses to refuse the subpoenas. "Muddying the waters", so to speak.