I never visualise the words written down. If I'm making an effort to remember words, it's more a matter of hearing than anything.
But I only reckon I know a song when I have the words coming out unconsciously like beads on a string; and the same with whatever I'm playing on the guitar, if I'm trying to remember the chords or whatever, I'm still some way from knowing the song.
Of course sometimes I put my foot out, and the next step just isn't there, even in songs I've been singing for yeasrs and know inside out. When that happens I fake it, either make up words to fit (which sometimes end up as the version I prefer), or singing the last line over again or the last verse, and just hope that people will assume that's how I meant it to go.