Bilbo's 'Black Mark' (Letter no. 246)

In discussing Bilbo joining Frodo on the journey to Elvenhome, Tolkien comments in Letter 246 (p. 328):

But [Bilbo] also needed and deserved the favour on his own account. He bore still the mark of the Ring that needed to be finally erased: a trace of pride and personal possessiveness. Of course he was old and confused in mind, but it was still a revelation of the ‘black mark’ when he said in Rivendell (III 265 [ = RK 6.vi.987]) ‘What’s become of my ring, Frodo, that you took away?’; and when he was reminded of what had happened, his immediate reply was: ‘What a pity! I should have liked to see it again’.

Yet we find what is perhaps the most enduring evidence of the Ring's effect on him in the Prologue, where the Prologue's author points out the persistence of the lie Bilbo originally told about how he came by the Ring (FR  Pr. 12-13): 

This account Bilbo set down in his memoirs, and he seems never to have altered it himself, not even after the Council of Elrond. Evidently it still appeared in the original Red Book, as it did in several of the copies and abstracts. But many copies contain the true account (as an alternative), derived no doubt from notes by Frodo or Samwise, both of whom learned the truth, though they seem to have been unwilling to delete anything actually written by the old hobbit himself.

So, despite saying 'I understand now' after he saw Frodo's reaction to his reaching for the Ring the night before the Council (FR 2.i.213) and despite saying 'Perhaps I understand things a little better now' (FR 2.ii.249) when he apologized to Glóin for not having told him the truth nearly eighty years earlier, nevertheless Bilbo left the original account in place, the lie, in his memoirs, leaving Frodo and Sam the unenviable dilemma of whether they should change it for him. This means that the first edition of The Hobbit is, therefore, a direct consequence of the deceptions and self-deceptions caused by the power of the Ring over its bearers. It is far more important, however, and far less amusing to recognize how subtle, how nearly invisible, and how permanent an effect the Ring has. Bilbo's newfound understanding, his apology to Frodo, and the apology he offers to Glóin and the other dwarves with which he begins his true and public account of the lies he told, do not prevent him from maintaining the lie for posterity. Understanding, regret, and shame cannot overcome the lie. (In a culture that prizes honor, being revealed as a liar brings shame.) Bilbo could not, it seems, even bring himself to ask Frodo to make the change for him. 

The near invisibility of these details should also help us see Frodo's struggles after the Ring's destruction more clearly. Think of how surprised Sam is that Frodo is going to take ship at the Grey Havens (RK 6.ix.1029), and how Frodo 'concealed' his illnesses from Sam (RK 6.ix.1023, 1025). Who would understand Frodo's suffering better than Sam, and who would understand this better than Frodo? Yet understanding is not enough. To be sure Frodo is protecting Sam, but the deceits that come with the Ring don't go with the Ring when it is destroyed any more than the longing for it. It becomes more remote but remains potent.