From the Early Days of DTL:

1991 and 1992 DTL PCs here. The circuit board on top is from October 1991, bottom is March 1992. I have two 1991s and one 1992 but one of the 1991s is going to Ryan. so that leaves me with one of each. NOS BTW.

Notice the lack of a year on the cover and the blue and black CdS eye instead of the lighter colored ones used elsewhere. Also, a round circuit board with fairly few components. All the DTLs are 1.0 ftc so are very sensitive. I suspect the ALRs are 1ftc too but the Ripleys are less sensitive (of course)