RNP,
YEs, it could happen. But there is a strong difference of level between B and C (C/I = 24dB), so the mistake might not happen that much.
But it will eventually, once in a while, so your QoS won’t be perfect: some HO will fail. Some call setup on cell B and cell C are going to fail. And also a lot of ghost RACH on cell B and cell C, which might lead to congestion.
Altogether, identical BCCH frequency on two cells that share coverage (even if it’s just a little bit) will degrade the QoS.