Thanks for the suggestion. No, the songs are not in my library online, as I'd expected was the case, and had already seen. (Because you asked, though, I just double-checked. They aren't there.)
I also don't expect any of these details make the slightest difference, but here we go. All of these were purchases from Amazon in MP3 format, since you seem to need to know that too.
Song A, 9.8MB, 254kbps VBR, sample rate 44.1 kHz, stereo channels, -4.5dB, id3 tag v2.3, LAME encoding
Song B, 7.3MB, 235kbps VBR, sample rate 44.1kHz, stereo channels, +2.2dB, id3 tag v2.3, LAME encoding
Song C, 16.7MB, 268kbps VBR, sample rate 44.1kHz, stereo channels, -2.3dB, id3 tag v2.3, LAME encoding
Song D, 8.1MB, 272kbps VBR, sample rate 44.1kHz, stereo channels, -6.7dB, id3 tag v2.3, LAME encoding
Song E, 7.5MB, 268kbps VBR, sample rate 44.1kHz, stereo channels, -8.2dB, id3 tag v2.3, LAME encoding
Song F, 8.6MB, 256kbps VBR, sample rate 44.1kHz, stereo channels, -0.4dB, id3 tag v2.3, LAME encoding
Song G, 8.5MB, 256kbps VBR, sample rate 44.1kHz, stereo channels, -3.0dB, id3 tag v2.3, LAME encoding
I should point out that I have literally hundreds of other songs purchased from Amazon with the same encoding (obviously different lengths, volume levels, and bitrates) but those all synced up with the cloud just fine. I'm going to go out on a limb here and assert that none of these particulars explains why these songs won't sync up.