None of the value changes in later trading mean squat to how much actual money the company gets to put in their bank account.

They get the money from the initial purchase of the shares, and never get another dime directly from the market again, unless they have another offering (which is quite possible). The stock price does drive leverage for later M&A and debt/credit activities, and matters to stock-based compensation, so it does have meaning, but the IPO provides a one-time cash infusion at the initial price.

They can issue new shares. It's not like it doesn't matter at all.