"Plus if a client has paid estimates then they are refunded the amount of SE taxes that they paid that could be deferred."

Here's why that isn't the case:

An employer that deferred kept the money and did not make a deposit. But, if they made a deposit and then wanted to defer, they were not able to get back money they paid. For the Individual, the money paid is part of their entire Tax payments, the same as Estimated or withholding. You don't "get it back." Once the tax return is completed, you get back any refund you are due, as usual. Not the deferred amount. It's not considered a Refundable Credit. It's simply a delay for not needing to pay what you owe until a later date.