Not sure what you mean by the 'slots'? There are the two fittings for the jack in the tool kit on the Coupe. Are there four on the Spider because of the less rigid body? Either way, I wouldn't put a trolley jack under them.
The four square attachments with the hole in the middle are in fact fittings used on the production line to fit the body shell to it's overhead cradle. It's a risky business using them as jacking points, though many have over the years.
The only official points for a trolley jack are the 'plates' below the rear bumper and to the front of the sub frame, but using these doesn't get the car very high. I use the sub frame near the wishbone, or to get even higher, the rear of the sub frame from behind the front wheels. At the back I use the centre fitting point for the link arms, but extreme care is needed to keep away from the link arms themselves, as these can be flimsy, and once bent even slightly your rear suspension geometry is gone.