Firstly, it should be noted that the act of assignment, the payment under it, and the rights and responsibilities of the concerned parties fall outside the scope of the LC, and UCP.
An assignment of LC proceeds ususally follows the process of the assignor (LC beneficiary) issuing a letter of assignment to the assignee. Assignments under English law, are classified into "legal" and "equitable" assignments. The distinction is that a "legal" assignment can only have effect if it relates to an existing debt, and the assignment is full and not partial. Failing this test, the assignment would be treated as "equitable" and most LC assignments would therefore fall into this category, i.e when the debt becomes payable, an equitable interest would pass to the assignee. It should also be noted that an assignee under an "equitable" assignment (unlike the case under a "legal" assignment) requires the assignor to join in, in any pursuit of claims against the debtor (the issuing bank).
Whilst a letter of assignment is given to the assignee by the assignor, the assignee must also ensure to issue its Notice of Assignment to the paying bank, so that the paying recognises the assignment. With multiple assignees, the situation becomes muddy, as unless each assignee is willing to be subordinate, the bank would pay whoever issues the Notice of Assignmet first.
More commonly, where an LC beneficiary wishes to assign part of the proceeds to more than one assignee, the assignor/beneficiary would instruct the bank to irrevocably pay each assignee a part of the proceeds in order of priority. Provided each assignee is aware that other assignees are involved, and its own ranking in terms of priority, the bank would acknowledge the instructions and amounts to each assignee, with a comment that since the assignor has already assigned part of the LC proceeds to other assignees, any prior assignments which the bank has been made aware of, would take precedence. The bank should also state that funds would only be paid, provided that they are freely disposable, that is to imply, there are no creditor attachments, court orders, injunctions, etc, which might prevent the bank from paying. Care should also be taken if the LC allows partshipments, since unless the assignment instruction is made clear (and does not contain a pro-rata payment clause) , in the event of a drawing for less than the assigned amounts, full payment should first be made to the assignee, in order of assignee priority.
In the given case, it is not clear what the terms of the assignments are, or the order of priority, but for the sake of simplicity, if A1, A2 and A3 follow in order of priority, the assumption would be that in the case of LC reduction, (and no corresponding reduction in the assignments), A1 should receive USD25,000, and A2 should receive USD5,000. That would still leave A2 out-of-pocket by USD20,000, and A3 by USD25,000, but that would not be a matter of concern to the paying bank.
My views only.