Andrew Burnett acutely points out that the weight standard of the semunciae of the first issue of cast bronze [sc. RRC 14] makes it clear that they represent a point of transition to the second, which is heavier than the first (the reasons are mysterious).
Holy variation, batman! But again four of our RRC 14/7’s would fit comfortably into the lower end of this observed data set.
Time to step back and ask a really basic question. How do we know its a semuncia and it goes in this series? I opened up Crawford’s list of the Nemi finds. Not one example of RRC 14/7. There are for context 50 specimens of other RRC 14 denominations including 11 uncia (weights for the four specimens in Nottingham = 28.19, 27.04, 26.77, 27.46, cf. weights of RRC 18/6: 19.96, 29.09, 24.86, 28.55). Jaia and Molinari 2011 (link above) have an appendix of all the hoards of just RRC 14 and 18 aes graves (i.e. those that should have an early closing date). No semuncias. Not surprising really, small change isn’t the most desirable for hoarding.