OK - for anyone that cares...
They did take the time to put all the letters in order...which is great.
Volume 1 is 1958-1965
Volume 2 is 1965-1970
Volume 3 is 1971-1986
Volume 4 is 1987-1994
So volume 1 & 2 contains letters from Screams and Living on Luck, volume 3, letters from Living on Luck and Reach and volume 4, just Reach.
There are editors notes at the start of each book, written (I presume) by Seamus Cooney.
Volume one has the 8 pages of letters - actual copies - like Screams. Likewise, all the footnotes corrections and explanations are the same as in the BSP editions.
I re-read with interest Cooney stating "I have transcribed and selected roughly 50%" of the letters available to me. Hmmmm.
Unless you were a real BSP nut, I'd say this is afar better way to buy the letters.
No, I'm not on commission from Virgin Books.