Not my point. If they had a vested interest in having Goldanna believe the baby was dead, which they clearly did if they paid her a coin and sent her away, well, it begs the question why she wasn't handed a dead baby if in your hypothetical there was one. Hard for a kid to deny that.
What she says is "they told me the babe was dead but I knew they was lyin'." Again, if they wanted her to believe the baby was dead and there actually was a dead baby about the place, it stands to reason they would show it to her.
Hypothetically speaking, the baby may not have even died. It's very plausible that the baby did live and was whisked away immediately. If Goldanna heard the baby cry, she would believe it to be alive. It's also entirely plausible the mother didn't die either. It wasn't unheard of in medieval times for a mother to leave her children, especially if enough coin was paid. Perhaps they told her Goldanna would be cared for and that is why they gave her a bit of coin and sent her on her way. Goldanna would have been maybe ten or so? Old enough to talk anyway. If she suspected or overheard someone stating something about "the king's baby", it would be best not to leave her with her mother and whom she thought was the king's bastard. Best to send the mother and baby away, tell the girl they both died and be done with it. Who is going to believe a common homeless girl? I mean, honestly, as someone who studied Tudor history, it isn't the wildest tale that has happened in real history, let alone fiction. Switching dead noble babies for common ones happened so much that noblemen started paying spies in birthing rooms, in case the midwife was paid off.
The Goldanna mission makes sense, too. If Alistair tracked her down, thinking she was his sister, how does him going to see her--as his sister--become inconsistent?
Also, someone mentioned how it was implied Alistair was born before Rowan died, because of the "concubine" statement. Now, I may be wrong, and if I am, then ignore this, but does anyone, including Loghain, mention she was definitely alive, or was it just implied because if that statement? I can't think of any definitive statement. If it is based on the implication brought on by the "concubine", it can be explained. They may have wanted to protect Rowan posthumously, not to mention her heir. She was a legacy, an icon to her people. They most likely wanted people to remember the image of the King who loved no one, could love no one, but his Queen.
Also, didn't someone from Bioware say the timeline was wrong and that Alistair would have been born after the death of the Queen? I could have sworn I read that when someone was complaining about The World of Thedas timeline.