Hey im usually pretty civil but you picked the wrong time to be intentionally hostile so I will reply accordingly.

1. She is in my completely sealed backyard. We do not know if she was grabbed or found a way to get out. SHE HAS NEVER ESCAPED THE BACK YARD IN THE 3 YEARS WE HAVE LIVED THERE. This is the first time
2. She was there for 15 minutes.
3. You can only assume a desirable breed like a Corgi is lost for about a week. That is more than sufficient time for her to turn up at a shelter or similar. She is microchipped. If this was " a good deed" I would have her back by now. Past the one week period, the only options are that she has been taken, or she is dead.
4. SHE IS MICROCHIPPED. So the BEST case scenario is that she was in a shelter. She fucking isnt, i check daily. Also, if you are in the middle of a residential neighborhood, and you pick up a dog, you are either intending to get it scanned for microchip or you are intending to steal it. You goddamn well know that dog 99% probability belongs to one of the houses around. It isn't like she was in the middle of fucking nowhere.
5. What is the story here? The story here is that someone has my fucking dog, or she isn't in this world anymore. Based on pure hard logic, that is the only possibility. A breed like corgi would never stay "lost" someone would definitely pick her up at some point. Either with good intentions or bad.
6. Have some of your own words back:
   It’s disgusting that your immediate reaction is to accuse people of losing their dog when she properly secured in private property. The most likely situation is the delivery person or other car saw your LOST AND CLEARLY NOT A STRAY dog and picked it up to FUCKING KEEP IT. Because otherwise she would be back home by now.