For how long was Thane on Illium?

If you talk with Thane while walking around Illium he says that he's been there for two years (Vista - near Liara's office).

However, if you talked to Liara before recruiting him to get more info about him, she says that he arrived a few days ago.

Which one is correct?

I don't know if this is something the devs/writers overlooked or if there's another explanation.