In my very humble opinion, the species that is truly most susceptible to RRD is R. wichurana. Multiflora gets the rap only because of the amount of it that is around.

If you are interested in budding, I'd definitely keep it as rootstock since it seems very healthy (my local multiflora tends to be chlorotic and manky looking). At least wait until it blooms next year to make sure it isn't something potentially interesting.

I think it’d be fine to keep around so long as you monitor it for RRD infection

I agree that it’s the sheer prevalence of Multiflora that gives it a bad rap. I do wonder if Double Knockout has now exceeded Multiflora in terms of number of infected plants. It gets a bad rap too, but for 2KO its mostly bad cultural practice and lack of education that makes it such an awful spreader of the virus.

Re ID: have you checked if your plant has fringed stipules - a distinguishing feature of R multiflora? (I've linked to a botanical drawing because it's easier to see them there than in the any of the photos I could find.)

I agree multiflora, Knockouts, wichurana are no more or less susceptible than any rose in your garden. There are just many more of them and they are not removed when they get sick. So at that point the virus is able to spread to them all.

Thanks you guys! It's going to be great to have all of the rootstock I need to try this budding chipping exercise. I guess I'll start a post on that in the propagation and start researching things. I think there are a lot of great tutorials over there that I've read in the past. I also have some good books that outline it in detail.

Countess DLC, it does have extremely fringed stipules. I thought I had better pictures of it but apparently not. However there still exists the possibility that it could be some sort of multiflora hybrid as my property had quite a few old roses originally that I still grow. It's just strange that I have two of these plants in strategic places. I cleared out one area and got some very unusual tulips growing there that I haven't seen the entire time I've lived here which is a long time. So I'm just going to leave them for the time being for cuttings and move them in the future when it's more convenient. They did already flower. You can see the tiny hips in the last picture. They were very few as it was covered by invasive Bush Honeysuckle and other assorted things.

Two apparently multiflora plants placed in 'strategic' positions in an old garden left untended for years, in an area where multiflora isn't usually found growing wild does sounds a lot like they could be understock from some long-deceased fancier roses, as I think you suggested in your original post. If you poked about a bit you might be able to see the old bud union somewhere around or just above ground level. If you really wanted to know, that is! :-)