The idea that single homeopathic ‘medications’ don’t always work seems like a post-hoc excuse to me. The example of Oscillococcinum is particularly unconvincing. For a start it is not possible to say that all the trial participants actually had the flu. The Cochrane Review uses the term “…influenza and influenza-like syndromes ...” for good reason.
The Review includes four treatment trials. Two of these are particularly problematic: Casanova (1992) was unpublished and Casanova (1984) was not published in a peer-reviewed journal, but a general medical magazine. The reviewers were also suspicious of the round number trial sizes reported (100 and 300). These trials, although larger than Walach(96) (the smallest of the final eight trials, n=98) probably wouldn't have come up in Shang et al.'s initial search because of their somewhat informal nature. It's pretty clear that they'd not have made it past the quality assessment.
The Review actually found insufficient evidence to say that treatment with Oscillococcinum works at all. In the words of the Review “… the difference between groups in the meta-analysis only just reaches statistical significance. It is arguable that a question as scientifically controversial as whether homeopathic medicines are always equivalent to placebo would require more statistically robust data …”. The authors concluded that “…Though promising, the evidence was not strong enough to make a general recommendation to use Oscillococcinum for routine treatment …”
Given the number of outcomes measured by the two journal papers included in the review (8 for Ferley 1989 and 17 for Papp 1988) the odds of getting at least one statistically significant outcome by chance alone are pretty high.
The Review also notes that “…Two trials (Ferley 1989; Papp 1998) pre-specified 'recovery after 48 hours' as the main outcome measure. The RR of being sick at 48 hours on Oscillococcinum was 93% (95% CI 88% to 99%) of that of placebo …”. Evidently a 95% CI reaching 0.99 cannot be safely considered to have reached statistical significance; that the main outcome measure did not make it into the oft quoted ‘headline’ for this review is another reason for caution.
Papp 1998 was included by Shang et al. in the final eight homeopathic studies (n=334). On the other hand Ferley 1989 doesn't seem to have figured in Shang et al.'s analysis, unless I've missed it. It would be nice to know why.
Anyway, I'd need a lot more to convince me that sometimes single homeopathic 'medicines' work and sometimes they don't. In fact Shang et al.'s Lancet letter demonstrated that individualised homeopthy fared no better than this kind of "clinical" homeopathy.