Circular 230, Section 10.28 deals primarily with physical docs, not electronic docs, which are only copies of the originals your client never relinquished possession of.  On that basis, there should be nothing to return.  Your focus should be the last paragraph, which deals with the tax return and your client's contractual obligations.

Going strictly by Pub 1345, you would have already breached the requirement for stockpiling.  But that's why I suggested reading that in conjunction with Section 10.28 of Circular 230.

Your last question in not relevant to your case as that pertains only to current year returns that were prepared prior to the IRS accepting returns by e-filing.  For TY2019, that was Jan 27, 2020.  That is because you can't possibly e-file a 2019 F.1040 signed on Jan 3, 2020, for example, by Jan 6, 2020 before the IRS started accepting e-filed returns.