Great post! Very informative.
I’d love to know more about the early-80s city (Leeds and Camden, etc) market jackets. Every post-punk band you see from the era has that same jacket - basically a LL 402 in sheep or maybe thin/soft cow with the sleeve zipper on the bicep. Looks like they had a lifespan of no more than a year before falling apart.
Frustratingly, when it comes to those sort of jackets, manufacturing was typically outsourced (from the UK, this was usually then, as is still often the case now, to factories in Bangladesh and especially for leather Pakistan), and batches rolled through under all sorts of ever-changing brand names. Some of the were quite decent, though my experience has always been that you might have to go through a few that were ostensibly the same to find the really good one among a bunch that varied from decent to bad via indifferent. It's always possible you might spot one kicking around second hand places in cities where they were popular, though given variable quality of manufacture, the survival rate also varies significantly. The nature of disposable fashion, I fear.... The bicep-based extra zip-pocket is an interesting little quirk. In part doubtless a notion that it would nod to without being too much like the Lewis jackets. (Lewis first added the forearm pocket to the Twin Track Bronx in 1966, before rolling it out across much of the line thereafter.)
The originals you mention probably were either lamb or low-end cowhide. Lamb has long been common in fashion jackets of this ilk in the UK - cheaper, and, crucially, thinner, lighter and easier to sew, thus bringing down the unit cost markedly. In my experience cowhide was always more common for these 'biker' styles, at least those made for men, though again for those built down to a price, quality varied significantly. Still, chances are of you can find one that has survived this long, it's likely fairly decent...