How much do the sizes vary between different sources for the same plant?

And when one is described as "nearly thornless" does that mean the whole plant from the ground up or just the flowering end of the canes?

I picked up a few cuttings from a pair of older plants that i "knew" what they were, only when I read more about them, they are not supposed to have big thorns and yet....ouch they do!

Ralph Moore's wonderfully thornless (the whole plant) has sported to a single flowered, thorny climber. Reine des Violettes frequently throws a thorny cane. Propagating from that thorny material has produced thorny plants. Grandmother's Hat and my Lynnie, often develop perfectly thornless specimen, yet some have prickles. Who knows why?

Many will increase their level of prickles as they mutate closer to climbing sports. Iceberg and Mlle. Cecile Brunner are excellent examples. The dwarf, bush versions range from lightly prickled to prickle free, but as they increase vigor and become more literally climbing mutations, the prickle counts and size of prickles increase. Prickles are a climbing mechanism and seem to be expressed in these two examples as such.

As for where they are prickle free, or more lightly prickled, there isn't a standard to rely upon. Some mean the whole plant, like Renae, Annie Laurie McDowell, etc. Some mean flowering stems, like Old Smoothie and Secret. Basye's Thornless Wichurana is without prickles...on the canes, but on the leaf midribs, there are sharp, small prickles, though some self seedlings from it lose those and are completely thornless.

At least with Iceberg and Mlle. Cecile Brunner, if you've encountered a particularly prickly one, they're likely to be larger plants, more closely resembling climbers. Look for ones without the prickles to get dwarf bush types. If the rose is supposed to be without prickles and you're propagating, don't use material with prickles as you may produce a strain that regularly expresses them. For the others, who knows? Prickles are the default. There are many more prickly roses than not. Some free from prickles result from seedlings; some from mutations. Roses mutate frequently and some fairly regularly. Until you know why they don't have prickles and what causes them to develop them when they're not supposed to be there, how can you tell what to expect? Kim

I had cuttings from 15+ year old Cecile Brunner climber, some thorns. And from what I think is an even older white version. It is climbing up over the back fence from a church yard and attacking those that walk too close in my friends yard. Those were some THORNS! And the friends would love my current batch of cuttings not to root so I can come get some more of it.