5th century cataphract from France- help needed

[Renatus]

Here are some questions for the epigraphists and, perhaps, the linguists. The K of Kl(audius) in this inscription looks like an oddly executed Greek kappa; the chevron (if I may call it that) is set too high up the vertical line. There is a similar, perhaps more accurate, character further down in karissimo. Harl, in the article that I mentioned above, gives the name as Fl(avius) but in that case the F is decidedly strange and (as Diocle in another forum has remarked) is preceded by a perfectly good E, so there is no reason for the stonecutter to have cut an F in a different form. Karissimo can also be spelled with a C but there are instances when both C and K occur in the same inscription, as here coniugi karissimo. A particularly nice example of the same formula with C and kappa is AE 1985, 110 below. In the present inscription, cataf(ractariorum) is spelled with a C but there are examples in which the same word is spelled with a kappa, e.g., CIL 3, 10307 = ILS 2540 or CIL 13, 6238 = ILS 9208. However, the use of kappa for K is not universal and there are inscriptions in which K is rendered in the form with which we are familiar, e.g., AE 1993, 1584 (in that case, in Greek skorpion).

So, to get to the questions, why are there all these variations? Are C and K pronounced differently, in which case, why should the same word be spelled with either letter? If they are not, why should both letters appear in the same inscription? Why should a Greek letter be used, when a Roman letter, although rare, is available? Is it a matter of local variation? Are there, perhaps, dating implications?

http://edh-www.adw.uni-heidelberg.de/edh/foto/F023655