Directly from the bill

IF A PERSON WHO IS ALLEGED TO HAVE VIOLATED SUBSECTION
(1) OF THIS SECTION ASSERTS THAT HE OR SHE IS PERMITTED TO LEGALLY
POSSESS A LARGE-CAPACITY MAGAZINE PURSUANT TO PARAGRAPH
(a) OF THIS SUBSECTION(2),THE PROSECUTION HAS THE BURDEN OF PROOF TO
REFUTE THE ASSERTION
"I owned this magazine prior to July 1, 2013"