You are not looking for a win. You are looking for a floor. The piece will name a date, a title, a figure, or a sentence they said. Your assistant drafted a friendly note that also asks whether they want to "add any context." That second ask is how a check becomes a negotiation, or a silence.
A fact-check is one question to a busy person who may not owe you a relationship. Write it so correcting you is cheaper than ignoring you.
One fact, as it would appear
Put the claim in the first lines, in the words you would use. "I plan to write that the plant closed on the 14th. Please confirm or correct that date." Then the source you are relying on, in a clause they can check — their earlier email, a public notice, a number they gave on the record.
Write for a cold reader. They may not remember your last call. They should not have to. Respect the time they have: a sentence they can answer in a sentence.
Do not hide a second claim in the same check. Do not ask them to bless a characterisation. Do not spring a contradiction and watch what they do. If you have a second fact, it is a second briefing, or a second paragraph clearly labelled as a second ask. A gotcha is a different job, and it does not belong on a channel whose point is a clean reply.
Make the correction cheap
Say that a correction can be one line. Say you will use their corrected wording for the fact, not for a speech they did not give. If you assumed the title they use now is the title they held then, put that assumption on its own line.
Do not attach the draft. RelayLink does not carry attachments. Describe the sentence. If your outlet requires they see more, send that where you already send copy, and keep this message as the confirm.
You approve the send. The note is yours. A nickname you use for them in a contact list does not appear in the package. Use the name they publish under.
They can answer from email, without an account
Most sources will never create a RelayLink account, and they should not have to. The briefing arrives as email and a page. They can reply there. If the address already belongs to an activated account, you need an accepted contact pair for a new thread. The refusal will not tell you which.
Give a time that is real for your desk. If you will publish without them at that time, say so without theatre. Silence is then a known outcome, not a trick.
What you do with the reply
Write back the fact as you now have it, and ask them to correct that one line if you still have it wrong. Do not expand the check into a new interview unless they offer one.
The piece can still be hard. The check should be fair. Fair, here, means they could see the claim and say no before it ran.