This is an important nuance that has not been picked up on much in recent weeks. Only one of the waivers of US secondary sanctions expires on 12 May; specifically the sanctions imposed under the National Defence Authorisation Act 2012 which provides for penalties on foreign (i.e. non-US) financial institutions that engage in significant financial transactions with Iran’s central bank. The majority of the US secondary sanctions which were initially waived on Implementation Day expire on 11 and 12 July; these are the sanctions on the provision of significant support to Iran's energy, shipping, shipbuilding sectors, or the provision of insurance and reinsurance, or refined petroleum products to Iran.
Does this matter? Perhaps. A failure to renew just the NDAA waivers might still provoke Iran to tear up the treaty on the spot. That could in fact be what President Trump hopes, allowing him to claim that it was Iran that broke the deal at a time when most of the other waivers were in place. But it also gives Iran the chance to affirm the deal and refer the initial breach on NDAA waivers to an Advisory Board established under the JCPOA dispute resolution mechanism for a non binding opinion. That would presumably be less than favourable for the US and might present Iran with a PR victory at a time when EU allies are already queasy at the thought of US sanctions targeting EU companies.
What is clear is that the staggered timing of the expiry of the waivers offers both sides some room for politicking and manoeuvring; something that both are rather fond of.
But some experts say the deal can survive even if Trump sits back and allows the sanctions that must be reviewed by May 12 to take effect once more. The potentially more important deadline, they say, arrives around July 11, when Trump must decide whether to reimpose a substantially larger batch of sanctions.