Is there a convention for figuring out the MSB and LSB on a counter IC?
I wish I could comment since I am not sure if this qualifies as an answer. Although maybe I could provide some insight to what jonk is really telling you. If you understand counters. You will know how their behaviour works. In other words: You can look at the Timing Diagrams and see which bits change during counting. The LSB will be the one that changes on every rising edge of the clock. (I hope I phrased this properly.) In the case of the 74LS169 you can look at the Timing Diagrams and notice that Q_a changes state after every cycle of the clock. Hence is the LSB