It's because when the cells don't match your criteria, the formula returns
FALSE...which equates to ZERO. So as soon as you have a non-matching
value...you get your minimum of zero.

Try this:

=MIN(IF(($A2<=Stock_Data!$A$3:$A$1616)*($K2=Stock _Data!$A$3:$A$1616),Stock_Data!$C$3:$C$1616,10^10) )

Remember to [Ctrl]+[Shift]+[Enter] to commit that array formula

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Regards,
Ron