You are right about an uninformed administrator QDROphliIe, and that does happen with admins who don't read very well beyond their model orders, but the uninformed party in this instance isn't the plan admin, it's the plan's counsel. When I pointed out to plan counsel that the order divides the already-reduced benefit into 50% pieces and leaves the existing SB alone, they agreed they understood that, but then insist that the 100% SB, (the cost having already been deducted from the benefit) must be only 50%. They want a result in which the AP's 100% SB magically becomes 50% of the as-paid benefit. And they're not arguing that's what the QDRO provides, they're arguing instead that that's what the plan rules require.
I don't conclude the plan is wrong in its general understanding of a how a 100% J&SA works, only that they defined it one way in the participant's benefit statement and in the plan document, but then attempt to claw it back if a QDRO divides the remaining benefit. The order's provisions define the SB separately from the "Member Benefit" (which I did not include in my cites of it above), so unless plan counsel is illiterate, they are deliberately ignoring it.
I think your synopsis of what you rightly term the ignorant view would be correct in a case in which it is clear a plan is misreading how a particular QDRO assigns a benefit. Here, however, it is clear from plan counsel's letters that they fully understand but are refusing to apply it, arguing that nonexistent plan provisions mandate the reduction of an existing 100% J&S if a QDRO assigns any other part of the benefit.
I know it's hard to wrap one's head around, primarily because it's complete hogwash, not to mention patently wrongful. And I will always avoid litigating if there is a better solution, which is why I'm posting, but so far I'm at a loss. The plan document lists the trustees but I haven't discovered who may be an actuarial advisor, or I would have reached out to them already; and the plan is self-administered as far as I can tell. No 5500, of course, which would help.
Sample of what should happen using imaginary numbers:
500 monthly annuity in pay status, already reduced to provide 100% SB
250 of that already-reduced annuity to AP via QDRO (only payable while the participant lives)
500 existing SB for AP if AP outlives participant (so not payable while the participant lives)
What result the plan wants:
500 monthly annuity in pay status, already reduced to provide 100% SB
250 of that already-reduced annuity to AP via QDRO
250 reduced SB for AP
250 of the participant's monthly benefit reverts to the plan
The plan just doesn't want to pay the full SB if there is QDRO affecting any other part of the benefit. One has to wonder why that might be, and none of the potential answers are pretty.