As Unitrade catalog denotes you should get a 4 sided perforated booklet stamp - as. The 925a is a booklet of 25. The asi is a booklet single like the as, but because it has the additional i, it has the straight edge, either left or right side.
The normal booklet contains a pane of 5 down x 5 across. Left side has 5 straight edges as well as 5 straight edges on the right. The middle 15 are fully perforated on all four sides.