No, there isn't. Most of the evidence you mention is anecdotal, or as you suggest, harks back to the 1920's, apart from the first and the final one you list. The penultimate one is again, anecdotal, but the writer suggests he is continuing to monitor the effects of geraniol, or at least the amount present in Ivy Geranium leaves, and its efficacy.
In truth, there is a commercial attractant which is more effective than geraniol alone, its combined with eugenol - the article below describes the attractant fully:
Youssef et al. 2009. Field evaluation of essential oils for reducing attraction by the Japanese beetle (Coleoptera: Scarabaeidae). J Econ Entomol. 102(4):1551-8. PMID 19736768, available online.
but the article itself is more about non attractants than attractants. It appears the commercial attractant is used to gather the beetles, then they're poisoned, rather than the attractant itself killing all of them. So if you were thinking a garden full of ivy leaved geraniums sited in full sun would wipe out the adult Japanese Beetle population, I'm sorry to say its not going to - but it might have some impact if other carnivorous insects get to the beetles while they're paralyzed.
You could download the information from the following link for interest's sake, but I think there's a charge for it:
Potter and Held 2002. Biology and management of the Japanese beetle. Annu Rev Entomol. 47:175-205. PMID 11729073.