1931 and 32 was the heart of the depression and Johnson was throwing any kind of mud at the wall to see if they could to get it to stick, meaning they were trying to do anything they could to sell motors unfortunately for them it was too little too late and they were bought out by OMC in 1935 😉

That numbering system (adding "5") does not apply to all models, as it does not completely fit with the "A" models

For instance – There’s no such motor as an A-30, the A-25 was sold in both 1925 and ’26. Nor is there an A-40, as the A-35 covered 1927-28.

it was only starting with the 1929 model year that Johnson advanced the model number by "5" on the "A" twins, with the A-45 being the last opposed cylinder "A" that was built. In 1930 the A-50 was brought out as an alternate firing twin, and the "OA" series was introduced as the smallest opposed twin motor in Johnson’s line-up.

Hope this helps.

best,
T2