No succeeding legislation was needed to change this. The 12th Amendment was ratified in 1804 to replace Article II, Section 1, Clause 3 of the Constitution. It was done to address the exact scenario you described in the 1800 election. A sitting Vice President who is a candidate in the presidential election has a blatant conflict of interest and has no business rejecting any electoral votes from any states.
Clearly there were AUTHORIZED slates in 1876 that were completely rejected, despite being "certified" by "someone in a position of authority." So that part is totally invalid.
As I understand it, the 1876 election would be an anomaly by modern standards for one important reason: the Southern states were still controlled by the Federal government and occupied by Federal troops in the post-Civil War Reconstruction period, so the political climate in those states was contentious almost by definition. That's why several states submitted competing slates of electors in 1876. Reconstruction formally ended with the Compromise of 1877, and the Electoral Count Act of 1887 was passed in response to the fiasco of the 1876 election and two succeeding close elections in 1880 and 1884.
There is no such thing as an anomaly in law. It’s called precedent. And no, the 12th Amendment did NOT change the veep’s counting authority, merely addressed the electoral votes from states so that you got a slate rather than two opposing individuals.
Yes ABSOLUTELY a sitting veep who is a candidate has a conflict of interest and ABSOLUTELY in 1796 it didn’t matter, and in 1960 it didn’t matter.
You are convincing me more and more of the correctness of my position.