Second, do you have another explanation for this visible evidence that one nonce series results in a stash of 980,000 BTC?
yea
The nonce was initialized to 1 in Bitcoin 0.1.0 and incremented monotonously:
tmp.block.nNonce = pblock->nNonce = 1;
[...]
if ((++tmp.block.nNonce & 0x3ffff) == 0)
as shown in block 12 that has same initial sequence but started later thus having a lower number. meaning both people started with the same nonce but the second person was behind due to starting later
it wasnt until an update that people began using their own random nonces. yet some noobs could have used the original v0.1 code and thus were using same initial sequence