I guess you can't connect them to wrong slots, but it's likely that they
don't sit correctly in the slots. We sighted people often need to mount
the cards without good view too, but we at least see, if the angle does
look good, something that can be hard to feel out.
Ask the most self-confident "noop" just to size up, if the angle of the
card does look right-angled enough and if there's any latch that is not
correctly locked in place.
Perhaps you need to loosen the screws for other cards, to ensure that
there's less tension. I had to do this and I also had to bend the plate
where the cards are screwed.
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