The letter+6 digit sequence has been in use since around 2004 starting with Axxxxxx. I think the sequence has since continued across all models unlike in the old days when different models had their own separate sequence. As is common knowledge here, CZ has always made the year of manufacture/proof readily known on the surface of it firearms. On pistols, it was marked in the area just above the extractor until around 2009 when it was moved forward on the slide closer to the muzzle. The Cxxxxxx started in the latter part of 2016 and as CZ made over 300,000 firearms last year, the C sequence should continue for another couple years.
Here are a couple of Czech army weapons showing the SN and matching year.
