Just started to write about the same as Brian last wednesday, but run away to finnish some work in the middle of the process and didn’t get back to it until today. I would just add one story of one friend who was restoring Ariel, I think it could be back in 70’s, he bought the bike from the first owner and thought it’s weirs the bike is chrome plated, just a handlebars were nickel plated. Buyer wanted different type of the handlebars than were standard, but this was only nickel plated on the stock.
I’m also often trying to find the period pictures or the pictures of the bikes in untouched original condition. I think nice pictures are of this 1929 Tourer sold at bonhams:
https://www.bonhams.com/auctions/19768/lot/286/
Of course, always could be some parts changed, modernized etc, but still very good source of the informations, I think.
All the best,
Martin