What do the numbers on the bottom of a Mason jar mean?

Many Ball mason jars have a number printed on the bottom of the jar, but this is a mold number that does not indicate the year of production. Rather, the mold number tells you where the jar was positioned on the glass-making machine that was used to produce it.

Is there a mason jar shortage?

Yes, there is still a canning supply shortage in 2021. It is this part of the two-piece lids that creates the seal during canning, and though jars and rings can and shouldnt be reused for hot water bath or pressure canning.