Ok Since I own a Holding Company , the way it worked when I Separated the company between Real estate and investment companies. I had 1mil shares of stock in HH Inc. I separated the two and created Diablos Ventures. I transferred 500k shares of HH Inc to Diablos, and created value in Diablos Ventures without dilution or adding AS.I maintained HH Inc as parent company. HH inc bought the 500k shares or holds the shares of Diablos until payment is complete for loan, which will never happen. So in reality to answer your question without AS addition, HH Inc maintained the shares and the value stayed the same. Now if Diablos has an investor then I would sell shares to entity. But HH Inc would maintain the share ownership and Diablos could increase value of HH Inc. This is the structure I used, not saying will be the same for AMBS.
AMBS could split and create new AS for other company. Woulod be approved by shareholders. This would increase value in one company and dilute the other, but if AMBS maintains Holding structure, then there would be no dilution without AS addition.
Not sure if this correct for public company, but my lawyer structured the separation this way for private company.