And it's also another one of your "possiblities" which when examined is absolutely ridiculous. It requires a series of accidents which would somehow cause a single batch of letters to somehow break into TWO batches of letters which would somehow be sent to New Jersey, which would somehow end up with ONLY the letters containing the crude powder somehow being sent out first, while the second batch (with the sophisticated powder) somehow sits around for three weeks until it somehow gets put into the system, too. It requires that this SERIES OF MISTAKES would somehow miraculously result in the senate letters being postmarked in the SAME area identified by the RETURN ADDRESS on the letters.
Everything you say is based upon the idea that it cannot be proven to be impossible, therefore you are free to believe what you want to believe.
It may not be impossible but it is also totally preposterous.
Individual customers do take 2 letters and bind them together with rubberbands thinking this helps them travel through the system faster ~ and we know that the tape used to wrap ALL the addressed pieces that were found came from the SAME roll! (Note: indicating they were prepared together at the same time and probably mailed at the same time).
"Used" letter mail or flat mail trays that end up in South Florida are shipped North to Eastern Pennsylvania and Central New Jersey.
We are not talking about rare or unusual events.