"Lot #" Labels on USA-Made Vintage Clothing

[FutureBlues]

Hello,

Apologies if I missed this somewhere, am trying to find information on this and couldn't anywhere - does anyone know what it means when you see "lot" and then a number on vintage clothing? I see it all the time on USA-made clothing, usually when there is a union label and am just curious. Attaching an image here.

Thank you!

 

[cotmyey]

Usually, the 'LOT' is associated with a specific factory and production shift. Tells the manufacturer something, but not much good to us.
I think they became phased out by a lot of producers in the late 70's when a lot of the factories went overseas.

 

[northstarvintage]

I always thought it was the size number, but I see in your photo that that's given as well, so Gayle's explanation makes sense.