This set of watches has for a long time been the least sought after of the T marked dials, but this has changed, and that mantle has been passed to the later watches made up until 1994 (I believe) and these watches can have attractive patinated tritium, but no date mark in the case back and slightly different dial pattern
The main difference in this group is that from -74 there is no dial step.
The -74 can be found with both a stepped dial, and a domed dial. As of now (September 2019) I cannot find a definite correlation with serials and dial specification. I can say that -76 and -78 must have a domed dial to be considered correct.
All have a DN90 bezel, and these are becoming harder to find in good condition. Identify bezels here. All are fitted with the square end chrono and have T SWISS T marks on the dial.