This is something I've been mulling for a while as a lot of vintage stuff I favour at this time of year to be 'on the border' of Americana and Ivy, I've kind of generalised it into what 'blue collar' workers would wear for work and 'white collar' workers wear for leisure - not a very accurate description but gives a broad 'ballpark' of my usual fall/autumn wardrobe.

Also the way an item is worn can mean it fits in a few 'categories'.
Pendleton board shirts are an example, although fitting in a few categories, the context they were worn in changes.
They were originally advertised as a warm winter shirt (tucked into your strides from the advert pictures, in a very 40/50s style with deeply pleated 'peg top' trousers )
but became a worn 'oversize' light jacket (in a Beach Boys style with hi-water tapered jeans and a t-shirt).

Speaking as an American, Americana is more classic American clothing, the stuff I used to wear like jeans and white tee's and Dickies, etc... Ivy is pretty geographically in time period specific.

Although Formby is right I think the point AC is trying to make is missed Americana and Ivy under their modern guises are two different schools of style.

I'd say they cross like Ivy and Prep do, but a keen eye for the details would make things clear in what camp someone resides. 

Ivy to me is the smart campus or business style relating to the soft shoulder.

I could wear some rhinestone tailored jacket and be Americana, clearly not Ivy. Bit then I could wear a bd and a pendleton and then there is a foot in both camps.

It's a fluid transition between the two because the original garments coexisted alond side eachother. But I suppose we have to expected the revisionist thing that goes on.

My current love is the 50s and 60s Americana that stretches to the Japanese Suntribe look and GI influence.

Ivy to me however is the non gimmicky classic style I use as a basis to add less future proofed Americana items to.

Yeah, plenty of guys mix and match the styles today, just as you would have likely seen a fair share of genre blending in many a man's wardrobe back in the heyday of the styles.