Because I do not yet control space-time

Do you know that I have funny stories about my work, but I feel I can't share them with you?
I would love to go into great detail about these, but I fear this outlet is not anonymous enough to protect the sensitive eyes of possible clients.

I will give you the short version:
I work in advertising, assisting the completion of up to 5 publications at a time. One of these is weekly, and printed a full 4 days prior to the date printed on the cover. Our deadlines for each issue fall in the previous week, to ensure that we have enough time to organize a layout, arrange for any ad changes, and to give us a small overnight cushion between printing and shipping.
On a day when my boss was absent, I recieved a call from an upset client, claiming a problem with the hot-off-the-presses issue. I whipped out my copy, bracing myself for a copy error that listed a wrong number, email, contact name, etcetera. Expecting something huge and evil that could seriously affect a client's business, right?
Wrong.
"Alright, I've got my copy open in front of me. What can I do for you?"
The client wants in this issue.
I am shocked. How can...? What? Surely not. Surely there is just a confusion of issue dates and they want in next week.
Wrong.
The client discussed the matter with my boss, and was assured they could be in the issue of their choosing.
Oh crap. This is bad. Did I miss a call? I am now frantically scrabbling through my desk. Looking for an overlooked post-it, or email, or blood trail with message scrawled in life-juice.
Customer is becoming upset. This issue should include their ad. What can I do about this? (They are becoming upset, probably, at my quiet freak-out, instead of smooth explanations. I've worked on that since then.)
I am still kicking files apart, for all the world like an addict seeking out that final "in case" hit. People could be getting shot and I would be shaking the computer in an attempt to jostle some information on this client into functionality. What to do? Should I offer a reconciliatory free ad? Do I have that authority? Was it even our fault? Wait....wait a second.
"When did you discuss this with my boss?"
Last month, it seems. And again, a week or so ago. Did they tell anyone they wanted the ad then?
No. The decision had not been made at the time. It was made this morning.
Oh. Relief, like a sweet breath of air in space. Now I simply have to find a way to gently explain our processes to this person.
"I am terribly sorry, but as I told you, I am looking at the finished issue now."
Yes, they are aware. They'd like to be in this issue. Still perturbed, but very professional and direct.
"Um...my apologies, but the issue is printed, and being distributed. I can get you into the next issue without any problem."
Nope, that would require a new decision. Can we simply not slide them in? (Now, I am grateful that this person is still trying cajoling tactics. Sometimes people are angry when they have ad-emergencies.)
I am sorry, but it is not physically possible to go back, put your request in, and then print all the current issues to include your placement. Why, you ask?

See title.

This is seriously like calling your old high-school and telling them that you secretly wanted to be in cheerleading, so can they arrange that? You'd like your photos taken in high-school and distributed in your senior yearbook.