Searching "aliquot castra" I happen by luck to find an old article (Rand, Edward Kennard. "On a Passage in Virgil's First Eclogue." The Classical Journal 2.3 (1907): 125-128.). in which the issue at hand is mentioned (tersely unfortunately).
In that paper a passage from the Ecoluge is dealt. For our need however, the relevant line is:
post aliquot mea regna videns mirabor aristas
The word arista: when appears in plural might mean harvest. In that sense it is very similar to castrum that its plural has singular meaning.
Now, it is without question that aliquot aristas should be taken together. The question is whether aristas following aliquot might have the plural meaning of harvest and thus yield the meaning "(post) several harvests" i.e, (after) some time. Or aliquot aristas should mean several conrns (i.e, the singular/regular meaning of arista). We read in the article:
Arista means "an ear of corn," and the plural may well mean "a harvest," as Conington admits. He thinks, however, that aliquot distributes the new singular again. But how would the Romans say "several camps," if not aliquot castra? Claudian thought the new meaning of the plural so much of an entity that he modified it by the ordinal decimus, not by the distributive, as the rule enjoins. (emphasis mine)
So it seems the author and other modern and ancient commentators did not seem to be alarmed by the fact that aliquot is used together with the plural-meaning (harvest), as they seem to acknowledge no other alterative of saying this like aliquoteni. Claudian even departs from the Law (A&G 137.b) above and use decimas he views harvest as a single unit. Even Conington, who interprets aristas here as corn, apparently didn't come up with strong grammatical argument to rule out the meaning of aliquot aristas as several harvests.
So overall it brings some evidence that aliquot can be used instead the theoretical aliquoteni (gives rise however to an ambiguity - that hopefully should be solved by context, though in this case from Virgil the context wasn't strong enough.)