I run a website that's in a similar situation, and it sounds like the author is close to the correct solution, but needs to take things one step further:
There needs to be a Single Point of Truth, and it should not be your little website.
BigCentralThing should be the official database that knows about where all the Whatevers are. Your little Whatever Locator site should only ever _pull_ from them. Need a new Whatever in the database? Get BigCentralThing to add it, then pull it in.
As an example, I run https://bettybeta.com/, a select guide to bouldering in Fontainebleau tailored for Women and short folk. We have a list of boulder problems in our database, but no way for anybody (even an admin) to add a new one. Every boulder problem record includes a link to its page at https://bleau.info/, who are dedicated to cataloging every climb in the forest.
Bleau.info is the Single Point of Truth. If one of our users does a First Ascent and wants to log it with us, we'll point them at that other site with instructions on how to get their climb in there, and tell them how to get us to import it. Any other path would lead to our database and the "official" database eventually diverging.
There are half a dozen other websites doing similar things to us. Some do what we do, but the ones that don't quickly find themselves out of sync and end up with a lot more work on their hands.
It's tough because, as the author says, writing the flow to import at our end is really easy (I've written it, before coming to this realization and hiding it again). But doing it is a trap.