By any chance do you still have the seed packets for those ? From the FAQ's from this forum ...

This is very helpful information from Mel's website on converting standard seed spacings to sqft spacing:"Depending on the mature size of the plant, grow 1, 4, 9, or 16 equally spaced plants per square foot. If the seed packet recommends plant spacing be 12 inches apart, plant one plant per square foot. If 6 inch spacing; 4 per square foot. If 4 inch spacing; 9 per square foot. If 3 inch spacing; 16 per square foot."

no idea on the cress.

Mustard greens depend on the variety, but I do most at 4 or 9 a sq ft.

Cilantro would probably be 4/sq ft. I grow mine one per hole in the cinder blocks on the edge of the garlic patch since it tolerates that stressed growing space well.

Malabar spinach was a sprawling thing. I would put it on a square near a trellised plant (like pole beans) so it could use the ground space as it spilled out of its square. Can't remember the spacing, I have not planted it for a few years.

Your seed packets give you the ultimate size of the plant. Use those for spacing ideas, as per angela above.

Dan