The US has also been working on improving their bunker busting bombs. And I believe the US and Israel are probably well into Iran's computer systems again and have all their emails and phone conversations well monitored. They must have been accumulating tonnes of data all about the locations of material and key personnel. Last time they were able to control their centrifuges and spin them out of control. They no doubt have saved their best tactics for later and can probably shut down a lot of systems remotely by now if they need to but we will never hear about this.
Maybe this is why the US has been willing to negotiate as opposed to Israel who has not.
splurge