Ah, yes. Well, you've picked out the most obvious inconsistency right there.
Of course, some people think that we shouldn't iron out the inconsistencies because that spoils the books. I disagree, because I think seeking to iron out the inconsistencies does the Chronicles the honour of treating them as real chronicles. I started a thread not long after joining the forum called
Hermeneutics in Narniology in which I discussed the methods appropriate for doing that.
Accordingly, in response to contradiction 1, there are two main possibilities. One is that the LWW version is drawing on a Narnian folk legend that arose to explain the mysterious disappearance of the Kings and Queens from Narnia, and is therefore not an accurate account. This could be argued on a number of grounds, one being the mysterious White Stag that seems like a legendary creature rather than real history. I also find it implausible that a lantern that had been standing from the beginning of the world, so as to be remembered by Jadis as significant in pointing the direction to the world of men, and being so significant to the entry of the Pevensies into Narnia, should have been forgotten.
The alternative possibility is that it is the HHB version that is inaccurate, an interpolation by some editor guessing at the kind of thing that might have been said at such a banquet. This view has much to commend it, particularly that the White Stag reference is also repeated in PC ch 2 by Susan in giving an explanation as to how she lost her horn. That would mean that, if the LWW version is incorrect, the mistake must have been copied into the records of the return to Narnia as well. Also, if the LWW section is incorrect, this also raises questions about how the Pevensies did end up leaving Narnia.
On balance, I would be inclined to regard the HHB version as the more suspect, though I have my doubts too about the complete acccuracy of the LWW version. Of course, there is one other possibility, in that LWW does not say how long they reigned. It could be that the exit from Narnia took place some decades after HHB, by which time they genuinely had forgotten. However, this seems unlikely, if she remembered the story for what must have been at least a decade (judging by Shasta's apparent age).
There are a number of inconsistencies between TMN and LWW. I'll pick up on a couple.
2. No explanation is given as to how Jadis acquired the rights to the blood of any traitor, and a surface reading of TMN would seem to count against her acquiring such rights (though I did attempt to address this in my thread
Jadis's rise to power).
3. It is unclear why Professor Kirke was not more open with the children in LWW about the fact that he had been to Narnia himself.
Peeps