I have been searching for an answer to this question for a few hours with no success.
Then I found your testing of multiple vests and plates regarding the SWAT members inquiry.
I have several level 2 inserts from older vests that are in good (unshot) condition.
I am debating weather to use them to make spall envelopes on hard plates or use a few to double up in a vest.
Have you tested to see what the effects of adding more layers of material to an existing insert would be?