Stacked PCB connections, split up current?
When you consider current rating of connectors, they are usually tested with conservative criteria: maximum voltage and a target operating life that is sometimes 10^5 operation, sometimes much less (100-200 operations). This target operating life depends o the intended use of the connector, so this may give you additional margin or none at all.
This said, for the typical Harting-like board-to-board pin headers, you may use more than the strict maths, as @Transistor says. Also, take into account the return (so + and -), possibly separating a bit the pin pairs (1 + always with its 1 -) to help dissipation and avoid hot spots.
Since such pins are from EMC and signal integrity viewpoint a &quot;ground&quot;, they help the shielding of signal lines, normalizing signal transmission and reducing crosstalk.
So, with 10A flowing between boards, allow let's say 3 pairs (+ &amp; -): 2 may be placed at the extremities of the connector and one pair in the middle of the pin array (assuming 2 rows, so + and - facing each other).