I'm going to assume that "country style ribs" are the ones where you cut them apart first before cooking ... I'd wager a guess that everything is near bone, and a thermometer might have problems with this particular dish. If nothing else, as you can't insert it deeply enough into the thing you're taking a measurement of, there might be enough conduction along the probe for the oven temperature to throw off the reading.
Could you tell us how far the probe was in the meat? I'd assume anything less than about 1/3 the probe might be problematic, with 1/2 or more being better.
...
All of that being said, are you sure it's an issue with the placement of the probe, and not a problem with the probe itself?
I've had a number of them go out over the years. I've actually given up on them, and gone back to an instant read thermometer, as I'm up to 4 of the bases (can still use 'em as a timer), and no working probes. (if anyone knows any brands that sell the replacement probes individually, or even better in multi-packs, I'd be willing to go back to using them)
To calibrate -- mix some ice water, and put the probe in there. It should read 32F or 0C. (if it even goes that low, not all do). Boil water, and read the temperature of it, and it should read near 100C or 212F (possibly lower, if you're above sea level). Compare it to another room thermometer after it's been sitting for a bit ... they should read the same.
Don't try to put it into the oven directly ... you could melt the probe ... that's how I lost the first one, so you can't try to compare it to your oven thermometer.
As far as I know, Collagen starts to break down below 60°C/140F, time play a big role, i.e. to get the same breakdown at 60°C as 80°C you might need 24-48h instead of 3-4h.
The higher the heat the more the meat is contracted and it will get dryer, in a stew that might not be as obvious as in other cooking methods but it should still be the fact. Compare tough cuts of meat cooked sous vide at 55°C-60°C for 24-100h, they get very tender and moist.
So the benefit will be moister meat. I think you must cook the veggies at much higher temperature (80°C-95°C) so you would have to separate the two. If the end result is worth the effort I do not know, I have wanted to try doing a 'stew' with meat cooked sous vide at 55°C - 60°C for 24h+, with the veggies done on the side at 80°C-95°C, normal stew style, to see if it would be better, but I have never tried.
Sources
Hum, I'm sure you or anyone can find enough sources to argue that you need 70-80°C(160-180°F), see e.g. On food and cooking(2004) pg 163 "...Meats with a significant amount of tough connective tissue must be cooked to a minimum of 160-180°F/70-80°C to dissolve their collagen into gelatin. "
The only potentially credible and official (what do you mean by that?) source that potentially can trump On Food and Cooking is Modernist Cuisine, I will quote.
MC 3.78-79 "When meat is cooked at temperatures above 50°C/122°F, a different chemical reaction -- the conversion of collagen into gelatin -- becomes prominent." it continues and says "Cookbooks and some scientific sources commonly claim that collagen converts to gelatine "at" some particular temperature. Usually the cited threshold lies between 60°C and 75°C / 140°F and 167°F. In reality, the hydrolysis of collagen is simply another example of a chemical reaction whose rate varies exponentially with temperature." it goes on describing that the exact temperature have not been measured and that it depends on what type of collagen, e.g. breed, cut and age. Finally it says "Tough meats can be cooked until tender at any temperature above 55°C/130°F (and even a bit below, if you are patient enough)."
Also see lots of sous vide recipes on the net saying that you can cook tough meat at much less temperature than 70°C/160°F and get it very tender. Or try it, I have and it works!!! I have stopped eating primary expensive cuts, flank, shin and brisket tastes much better!
See also SAJ14SAJ reply and Stefanos comment below, as per Baldwin which should be almost as good a source as oFaC and MC
Conclusion
The answer to the question, "how low can you go and still get collagen break-down" I would answer 55°C/130°F or even a bit lower. That is NOT a realistic temperature for cooking a stew, especially not if you will put veggies in it, but as far as collagen breakdown goes that is the lowest temperature for 'stewing meat'.
Best Answer
Even if a pig ate something like that a piece of jewellery wouldn't end up in the muscle (meat). It would pass through and out the other end; if it didn't have time to do that it would still be in the digestive system, which is removed before the meat is cut into portions (if you'd said dog food it might be another matter).
I suspect that it entered the dish sandwiched between two strips,or pinned into a side of a piece that you didn't see. If you cut across the strips to dice it, it could still get in. I know from experience with diced game that you can deliberately feel for shot and miss bits. That of course would be embedded, but you weren't looking for metal in your meat.
On the other hand, what liquids did you add? Passata/creamed/chopped tomatoes from a can could introduce something without you noticing it.
In either of these cases it was probably removed at the start of a shift in a food factory and transferred via clothing, as it had the back on it. In some liquid foods it could have come from the farm like that but most pass through a sieve at some point.
I assume you've checked that no one who spends time in your kitchen has lost an earring? Is hard to see how it could get into the dish that way, but not completely impossible.