It's not uncommon with film to set up a line, run off several master rolls, break down the line, set it up for another film, then run off several master rolls, break down the line, continuing to run through a bunch of products, eventually looping back to the first one. It's completely possible to manufacture a modern B&W emulsion on the same line as colour emulsions, many are coated in several layers, just like colour. For Kodak the odd man out was Kodachrome, it needed special manufacturing, which took a long time to set up. The master rolls sit in the freezer until there is a call for product, they take them out, thaw them, package them, and ship the film out.
Technically therefore, most products, except the ones in the coating plant, and the ones being slit and packaged, are no longer being manufactured. Now I just looked on Kodak Canada website for Plus-X, normally when Kodak discontinues a product, they post a discontinued notice on the website, there is no discontinued notice for Plus-X.