This was discussed elsewhere quite a bit ago, but just recently came up here.
Doubleday Gutter code theory:
Hypothesis- The letter in the Doubleday gutter code indicates the year the book was PRINTED. The number is the week of the year the printing was done.
Keep in mind a book could be printed during the last several weeks of a calendar year but not be released until several weeks later and thus be released in a different year than the printing occurred.
(This is for 1st edition 1st printings)
Carrie-------- Released in 1974. P6 gutter code 4=P. Printed the 6th week of 1974.
'Salem's Lot-Released in 1975. Q37 gutter code 5=Q Printed the 37th week of 1975.
The Shining RELEASED in 1977. Gutter code R49. 6=R Printed the 49th week of 1976.
Night Shift RELEASED in 1978. Gutter code S52. 7=S Printed the 52nd week of 1977.
The Stand released 1978. Gutter code T39. 8=T Printed the 39th week of 1978.
Pet Semetary released 1983. Gutter code Y38 3=Y Printed the 38th week of 1983.
According to Hill House:
QUOTE
Early 1977 saw the publication of King's third novel, The Shining.
That would seem to fit with my theory of the book being printed in early December of 1976(Assuming a M-F work schedule it would have been the week 12/6/76-12/10/76).