My good friend Skip took his hose off his 68Z survivor and no, it does not have any ribs. He's the 2nd owner and a local car just like his 69Z. Car was taken off the street around 1973/4 so we have a high level of confidence its the original piece. Note the hose skin look!
Steve, thanks for other data point. That clamp change will remain a mystery.
https://live.staticflickr.com/65535/...3cb2997e_b.jpg

https://live.staticflickr.com/65535/...0b568e22_b.jpg

67 Chevelle survivor and it does not have ribs.

I'm not expert in PCV hoses but could there have been
a few different vendors that supplied Chevrolet with their
own hoses? Maybe that could be why you have both a non-
ribbed hose and a ribbed one?

Sal

Btw, I saw this on ebay today...

https://www.ebay.com/itm/67-68-69-70...MAAOSwu-telQZn

Yes. Most everything that was supplied to a plant had a least 2 suppliers.

Of course agree with Darrell, but the sampling even thou small leans toward ribs not as common on say a 68 like a 69. Hopefully we can add more info as time goes on.

I checked my unrestored 69Z. Looks to be original ribbed hose. 08C (late 69)