It’s fine… thank you for sharing all the info 
I don’t have another sensor to use, and I have this thing until the 23rd so I am leaving it alone for now… it actually did catch a low @ 50 earlier and was tracking almost spot on with it (took FOREVER to get back up… 24g juice box followed with a PB&J sandwich that was about 45g carbs, and after 2 hours I was only around 118.
I have gotten LOTS of ???, mostly overnight, which I think may be from moving around or sleeping on the sensor, but any time my BG is changing rapidly, Dex seems to just give up.If you spend a few hours searching for posts re: "What changed when I did the upgrade", you'll find that nearly everyone has enjoyed VASTLY fewer instances of "???" with the "plus" version. (It might even be 100% of people who noticed a difference. But if it's not, it's very, very close to that.)
I don’t know if I mentioned it on this particular board, but long ago, when I first used the original SEVEN and hated it, I asked support to send me raw data for a group of “???” periods which I had found to be suspicious (daytime, not slept on, and without sudden leaps on fingerstick.) As I had suspected, the “missing” raw data values were consistent with the values before and after, the Receiver would have shown a very smooth and steady curve if Dexcom’s SEVEN had only been willing to report the results on-screen.
I know a little bit about device microcode (and in fact, have been well paid to analyze and fix this stuff in the past, working full time for some computer OEMs.) I did quick look (followed by a slightly longer think, fueled by strong Coffee and a Snicker’s bar-- the traditional 3 AM foods of computer coders. properly Bolused, of course). Next day, I called up Dex and discussed my assessment, making guesses (with very high confidence) about the ways in which the Dexcom’s calibration process was leading to a badly-fit calibration curve which the STS hadn’t been creating, even though it had used the exact same code. And how, ultimately, the bad curve led the Seven to frequnetly declare nearly perfect readings as “mismatched, too flaky to report”, even in cases where the bG and raw data had barely moved at all from the previously displayed dot.
The PLUS is vastly better at fitting a calibration curve, and will almost certainly have provide you with fewer periods of “???” AND vastly improved accuracy. Did you boil that old Seven and get a “Plus” yet? If not, I’ll again suggest that you fire up the stove. Or, just toss the Receiver into the sink for a few minutes, either way works… :))
Yes, all 3 machines (MM, Abbott and Dexcom) need that additional reading from a variant bG to begin “locking in” a custom curve. Without it, they will match up your value with a pretty much un-customized “default” slope into a standardized X-intercept, and/or values mostly based on your your previous, nearly worn-down-to-nothing and now thrown away Sensor. Total suckage either way. You had also already caught your breakage of rule #1 (never, ever enter give it data during a rising bG), a very nice catch indeed!