Please note that Uddhaava Gita is not a separate scripture, it's actually part of Bhagavata Purana: Canto/Section/Skandha 11. Similarly, Bhagavat Gita is also not a separate scripture, it's actually part of Mahabharata: Parva/Book 6 named Bhishma Parva.
But these Gitas mainly studied as separate scriptures. Historically, Bhagavat Gita got attention from more scholars and we got fixed number of chapters and shlokas in most of the edition but there are different recensions of many scriptures and Uddhava Gita is not an exception here.
Same is pointed out by another user Swami Vishwananda in his above comment "there are different recensions of many shastras, including the Uddhava Gita.".
Now, let's see the differences in the links mentioned by you in the question.
The first link [pdf file might get auto downloaded on clicking this]
The second link [pdf file might get auto downloaded on clicking this]
So this link treats whole Canto/Section/Skandha 11 of Bhagavata Purana as Uddhava Gita. This can be observed from the last page also:
The third link
By reading any of the version, you can get main part of Uddhaava Gita.
But if you want to understand more background, read whole Canto/Section/Skandha 11 of Bhagavata Purana.