Hi Peter.
A lot of these details have been lost over time, and as you said, Howard only got into the business during the MkIII days, so even he isn't 100% on everything.
I know both MkIs and MkIIs came with dot and bar style displays. I think they started using bar displays late with the MkIs, and then when the MkIIs came along they just used whatever was handy.....bar and the leftover dot style. Howard used to say they had a lot of trouble with quality control, and the workers just used whatever they could get their hands on.
In my mind there are 2 differences between the MkI and MkII. Speed adjustment (either trimmer or electrical), and the leap year cycle display. MkIIs display a number with the running seconds, and the MkIs show a dot to indicate leap year (Howard told me this). I think this dot indicates you're in the year with 29 days in Feb.
Hang on, I've just though of a 3rd difference.......you can adjust the month on a MkII as well
Rgds.