[DavidG]

The '37 lenses have '78' molded in the glass and as Mike indicates, the random numbers at the top, usually single digit, are mold numbers.

There are some who think that Ford paid its workers to sort the lenses by mold number so that they could be matched pairs. In an industry where every penny counts, the likelihood of that having happened is right up there with there will be no new cases of COVID-19 reported today.