That happens all the time there.
Any real life trade gets posted. Many don’t work out with their numbers and requiring “fudging” by adding money. A lot of them that don’t work out are actually pretty close.
Sometimes the values they use just are not realistic. But sometimes GMs make stupid deals, which isn’t really their fault. If the website existed at the time, I’m 100000% positive it would have never accepted that Shelby Miller-Dansby Swanson trade. But that wouldn’t be a flaw. The whole world knew that was a bad trade except one guy. Unfortunately for Diamondback fans, that one guy was their GM at the time (Dave Stewart, I believe.)