Both Yoshida & Co's "Porter" label and the brand Head Porter makes a variety of products belonging to the famous "Tanker" line. For the purpose of this thread, I'll be referring to Yoshida and Co's "main" Tanker line (ignoring offshoots like "Tanker Black" or the different anniversary collections), and to the "Tanker-Standard" and "Tanker-Original" lines by Head Porter.
1) First off, are there are differences between the lines of each brand? They are seemingly identical with many common items and I have no idea why an essentially same collection is made under two different brands, even more so considering Yoshida & Co produces everything for Head Porter - or so I've heard (more on this below).
2) Once and for all, what is the relation between Yoshida & Co and Head Porter? Is Head Porter a sub-label or sub-brand? Or is it actually an independent company? (that would be really odd because a. Head Porter shares a name with Yoshida's most popular label, b. I believe Yoshida is the de facto manufacturer of all Head Porter's products, c. Head Porter sells many of Yoshida's most popular designs - whether unsubtly in their original form or a variant of it, and d. Each Head Porter product is stamped with the famous "Yoshida & Company - PORTER - Tokyo Japan" label.