You're right. Primers that fall out due to pressure are "blown" and primers that fall out because the bolt starts moving too soon due to over gassing are "dropped" primers. I tend to use the term "blown" to refer to all primers that have fallen out even though I know I shouldn't.
I think our experiences differ a little as I've experienced both dropped primers on 4 separate AR's and blown primers on more rifles than I care to admit as I used to be a foolish subscriber to the philosophy "always run the ragged edge" on every cartridge I loaded.
"Swipe" marks as you suggested were indeed evident in each instance I dropped a primer, but I couldn't tell that they looked any different from swipe marks from over pressure. There might have been evidence I missed such as primer shape, but the two distinctions that really stood out to me from the dropped primers were: 1) The primer pockets were completely covered in powder residue 2) The primers did NOT fit back into the case. With blown primers from pressure I've always been able to put the primer back into the case fairly easily by hand and the primer pockets are always pretty clean.
Now whether any of my dropped primer observations are anecdotal to my experiences to date or apply to all instances I don't know. Nor do I know if they have anything to do with the MSR issues...
We might be talking in circles here, but I will say this. At initial pressure peak in a case with too much pressure, the case will swell too much and expand backward until the primer is loose. i've done this enough to know, like in a bolt gun, that pressure is the issue. Sometimes to the point, it will go right in and fall right back out.
I've also oversized cases to the point there is play between the shoulder of the case and chamber, and the case is pushed forward when firing but is not not pushed forward so much that the primer won't ignite. These cases, even with light loads, exhibit the classic high pressure loads because the case is suddenly rammed backward to the face of the bolt.
I have never had a gas system type rifle, with properly sized ammo, get slammed back so hard the primer pocket opened up. I've had many a 'swipe' because the pressure at the port (and back through the system) was high. While firing, the case is held tight to the chamber walls. If there is enough pressure to unlock the bolt early, then there is a swipe on the case. But, I have never seen enough pressure from unlocking the bolt early to blow the primer pocket out. The case itself can expand more than expected., but there is nothing to make the primer pocket expand, that wouldn't have already made it expand initially, except over pressure.
The excess throat as described in the pdf would be more inclined to alleviate pressure. Rather than take the 10k pressure from the port and blow primers out. A short throat on the other hand would be more inclined to increase initial pressure.
Could it be these are actually 'undersized cases?' That show swipe because the gas coming back has nothing stopping it, AND, its' moving early due to the gas burning too slow for the load and there is too high pressure at the port?