I recently purchased this typeface so I would be curious to hear a few answers to these questions, especially #5.
I'm guessing there is quite a close connection to the original drawings as the font comes with lots of alternate characters suggesting the indecision of initial drawings. (This is pure assumption on my behalf.)

As for your last point, Typowiki!

Typowiki is cool but can just anyone go adding to it whenever they like?

Hello Nick,

there are already two threads about P22 Underground Pro, at least:
In addition to the aforementioned Underground Unbound, announcing the PDF specimen, there’s Appropriate alternates or an anachronism?, started by Paul Hunt while the fonts still were in the making.
If you want to share your knowledge, I think it won’t be a bad idea to add it to either of these existing threads. And I second Andrew’s suggestion, the Typowiki is a good place, too. Yes, anyone can edit the entries, that’s the idea. Just start here: P22 Underground Pro. And then add a link to the list of Typefaces.
F

Thanks for those links Florian. Major kudos to Paul, it's one of my favorites.

(For the record I do not think it is anachronistic to add alternatives – surely it would be anachronistic not to include them! Anachronism is most annoying when it is unintended.)

Another version of Johnston I have been seeing a lot of lately is this. A better image here.

Notice the pinched tittle and vertical terminal on the 5. Anyone know which version this is?

This version that Transport for London use is New Johnston.

This is New Johnston Book (with the pinched diamonds). Have a look here.

I think it was done by Eiichi Kono as part of a Banks and Miles overhaul of the London Transport identity.

It's available from TfL in OpenType to suppliers.

It has to be one of the most effective corporate identities in history.

I meant New Johnston Book Bold.

'Book Bold'? I ask you.

Here are some more insights on New Johnston from the Edward Johnston Foundation.

If you love sans serif type design, then you need a copy of this book. (Johnston's Underground Type by Justin Howes, in case that link ever breaks).

Thanks Nick. Hopefully Paul will pick up the thread.

You might want to mail this to Paul, Nick.

1) Contact P22

2) P22 Underground and New Johnston share a common heritage, that is all.

3) P22 Underground is an attempt to revive the original type by Johnston retaining imperfections such as super-low contrast, the long tail on the l, &c. My rationale was that it is these 'imperfections' that give the face charm. New Johnston is a less-strict revival, but still retains many of the qualities of the original but has taken some liberties to improve the face for its purposes.

4) Persons listed in the credits on the PDF beta-tested the fonts, gave feedback, critiques or lent images for the PDF.

5) Not that I know of. The original type was a wood type, the nicked corners were incorporated to give a sense of softening of edges that might have been associated with the types having been made from wood. Otherwise, I included these as a design feature partially due to my own aversion of sharp corners.

If you have any other questions, you can post them here or email me:
paul (@t) p22 (d.t) com.

(1)
Licensing and design are two separate issues. The London Transport Museum granted P22 a license to use their intellectual property to recreate the original Johnston design for LT. LT has a very strong identity and IP protection. Even though the font was redrawn from "scratch", having the official licensing makes it an authorized "product". There are many reason this was the only way to go for this project.

(2)
New Johnston is the official face of LT as designed for them by Banks & Miles. It varies from the original Johnston in several ways.
P22 Johnston Underground was the basic font done in 1998. It is a very close facsimile of the original Johnston and doe snot follow New Johnston.
P22 Underground Pro is Paul Hunt's refined and expanded version of P22 Johnston Underground. It is less like the original Johnston than the first P22 version but more than New Johnston.

(3)
Overlaps with above answer. Sure call it a revival.

(4)
Paul did pretty much all of the Pro set on his own. I smoked Cuban cigars and stood over his shoulder saying: "Hunt...isn't that damned thing done yet!"

(5)
The corner bumping was something I decided to do for P22 Johnston Underground since we were working from woodtype specimens and I didn't want sharp corners at large sizes. It was an experiment to see if it would soften (and therefore make less digital) the overall feel of the font.

and now you have... the rest of the story.

Thanks Paul and Richard.