Originally the PLA2216 was delivered with 32 leads, 32 grabbers, 32 colored stickers numbered 1-16 and 32 black stickers labeled GND.
The stickers are to be placed on the flag like protrusions found at one end of the lead, one at each side of the flag.
Apparently at some point in time at RIGOL they decided to reduce this to 20 leads, 20 grabbers, 32 colored stickers numbered 1-16 and 32 black stickers labeled GND.
Why, probably to save a couple of bucks.
The leads for signal and ground are exactly the same, as are the grabbers.