It should be CENS, coin or die wear is the most likely explanation of why the letter 'S' is not fully struck up.
That makes perfect sense - thank you. I'm still wondering why there aren't hundreds of this coin variation out there, and why it's not listed in references. It's a very common coin in a very low denomination, so it must have been produced in fairly large numbers, I would think, being what I think of as a commoner's coin.
My hunch is that there are very likely more of these out there, they just go unnoticed, just like your present example until we caught it!
That was my thought as well - it's so common a coin and so low value that it just isn't likely to warrant any particular attention from others who own it. That's okay by me - I can call it somewhat unique until I get put in my place with other examples ! The other thought I had was that maybe, since this coin comes in three obverse variations (RIC 727, RIC 728, and this one, all with the same reverse), maybe this one came from a late run with this obverse die and just didn't see as much production as the other two dies. Just thinking out loud.