In some cases, at least, some dozen means "some twelve", not "some number of dozens":
- "some dozen or two of varieties" [link]
- "some dozen or sixteen lines" [link]
- "some dozen open-air localities" [link]
- My confidence about the meaning of this last one is because this book very frequently uses phrases like "some half dozen", "some three dozen", "some dozen and a half", etc., to the point that it seems to be an idiosyncrasy of the author. So bare "some dozen" is almost certainly part of that.
And while searching for the above, I also found this paragraph making the same claim:
But before substantives determined or to be conceived quantitatively some appears in the singular or plural, not so much to mark the fraction of a quantum, as the quantum itself, as indefinite, inexact, or approximate: My father had the full view of your flourishing style some hour before I saw it (Ben Jons, Ev. Man in his Hum 3, 1.). About some half hour hence (Shaksp., Cymb. 1, 2.). If I may counsel you, some day, or two, Your highness shall repose you at the Tower (Rich. III. 3, 1.). I would detain you here some month or two (Merch. of V. 3, 2.). Some dozen Romans of us (Cymb. 1, 7.). Bastards, some dozen, or more (Ben Jons., Fox 1, 1.). Some five and twenty years (Shaksp., Rom. a. Jul. 1, 5.). Some six years ago or more (Carl., Fred. the Gr, 5, 5.). Some four miles distant from one of our northern manufacturing towns . . was a wide and desolate common (Bulw., Maltrav. 1, 1.). Surrounded by some fifty or sixty fathoms of iron cable (Dickens, Christm. Car. 1.). All the ladies save some twenty score (Byron, D. Juan 8, 130.). If here an, a should appear instead of some in most cases, no essential difference, will arise. Some and an are distinguished syntactically by the formers answering, except with collective numbers, to an original plural form. [From An English Grammar: Methodical, Analytical, and Historical, by Professor Maetzner, translated to English by Clair James Grece.]
Here are some examples with hundred, thousand, etc., that also seem to have this same sense:
- Love be planted in my heart even the more, blossom and multiply some thirty some sixty some hundred fold. [link]
- At one instant they [="the broken clouds"] were suddenly cleared away, and discovered to the view a lake that lay probably some hundred feet below, and looking like a small basin of water, or a round hole through the world, so that the sky was visible beyond. [link]
- Seems to be giving an estimate; the "probably" would be strange if the estimate were not at least somewhat precise.
- The drive, some thousand miles, would take him two days. [link]
- The drive in question seems to be to Houston from somewhere in Arizona, so one thousand miles is a reasonable approximation. (And two days is a reasonable estimate for an unaccompanied driver.)
- In contrast, there are many incentives and attractions in receiving European and North American countries that have increased the number of skilled Arab migrants to some million.
- The same page uses "some 2 million workers", "some $232 billion", and so on, which is why I'm reasonably confident that it's this sense of some.
Also perhaps relevantly, the decline of some dozen, some hundred, and some thousand over the past 150 years correlates pretty well with the decline of the unambiguous some half dozen (see Google Books Ngram).
None of the above, however, demonstrates that some dozen/hundred/etc. never means "some number of dozens/hundreds/etc.". So the phrase could still be ambiguous. But I've found only one case where it does seem to mean that:
twenty-eight thousand and some hundred guilders. [link]
and the more I think about this case, the more I think it does actually mean something like "28,100 or so", with the same sense as the above example.