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There's Square back & Wedge back isn't there?

- The back panel on the Levis jacket. 

I've heard various things about all this. What's your take?

What does one signify over the other?

I should point out that I can't quite see the attraction of vintage Levis.  Or Levis at all.  Not now.  Around the time of my birth, yes.  But not now.

It's each to their own Raincoat, of course. I feel there is a romance and almost a social history woven into Levis.

I think this is where we begin 'crossing over': from pure Ivy into 'Americana'.  I have no great problem with that.  Clift I tend to see as Ivy, Dean as 'Americana'.  Elvis, I think, represented the crossover look pretty well: better than the 'Jivey Ivy' enthusiasts IMO.  John Simons offers bits of 'Americana': 'Prison Blues', for example, and I keep a few selected items of my own: an old Teamsters zip-up jacket, an old McGregor Anti-Freeze, a genuine garage shirt.  I spent one summer in 50s bowling shirts, worn with Levis and Weejuns - seemed appropriate for the fun fair at Skegness.  Ah, and I love my old Levis chinos!  Russell Street also once had a pair, very similar. 
I just feel that Ivy works best when obeying certain rules.

You're right with the "more eclectic Americana" Stacyboy. That's much more what i'm into rather than the straight ahead Ivy like a lot of you chaps.
Many of your discussions I love to follow because they overlap into my world of style and interest, but I could never call myself in any way "Ivy". The loafers, khakis and jazz I dig, but I also love old leather jackets and vintage workwear. I look more like a I should be driving you guys downtown in my yellow cab or mending the roof on your Aspen cabin, rather than meeting you for cocktails.
One thing is for sure I greatly admire your collective styles, your knowledge and your boundless enthusiasm.

Levis haven't been made in San Francisco, or anywhere else in the USA for years. Their loyal seamstresses were all laid off, the machinery shipped overseas and the heavy cloth dropped.
Old Levi Strausse came to the gold fields, bought some canvas and made up pants for the 49ers.
And the #1 cause of death was not Black Bart, but simple exposure to the elements. And that american knight errant, or error, the cowboy never wore those farmer's pants. They are hot, chafe in the saddle and give no thermal protection. Cowboys wore whipcord wool until Hollywood and popular fashion shoved his cultural successors into the things.
To wear bluejeans and be a 'cowboy' you buy Wrangler boot cuts several inches to long, iron a seam into them and then enjoy the corrugated ripple effect as they fall  over your boot. For full authenticity you have to shove a round tin of Skoal in the rear pocket and get the telltail circle fading. This does require the obligatory removal when actually riding horses and eventually mouth cancer.
Yee HA!

Levi jackets puts me in mind of Donovan (Remember him ? Thought not) or early Bob Dylan.

I am tired of blue denim now and too old for it - the Jeremy Clarkson effect.

Lee Riders and Wrangler are also quite nasty.

Thanks, Hank.  I know you know your onions!!

I thought what Mister Raincoat said about college lectures trying to be trendy by wearing Levis was funny, When a lot of cats on this site already look or aspire to look like college lectures or geography teachers.
Surely, if you didn't wear a certain clothing brand because arseholes wore it you struggle to find anything to wear at all. Is ever person who wears Brooks or Bass a fabulous switched on person I wonder?
You mix and match and find your own influences, take the best from here and there and avoid uniforms, stamp your own identity on a look. If everyone slavishly stayed within the pescribed confines of a style, be it Ivy or otherwise the style could never move on. But, then again some cats want to be frozen in time, but that can't be healthy.
I just wish that Jeremy Clarkson hadn't been mentioned, that really hurt.