What Could Have Been: Grimwood was working on a sequel when he died on June 6, 2003. He died of a heart attack, so one could hope he wrote it during his next replay...
Only four known replayers are found during the 1963-1988 era. Jeff, Pam, Stuart and the one from Australia who sent the cryptic letter Pam and Jeff received.
The Internet gives you to ability to watch the plot-important 1963 Kentucky derby - a luxury the author probably didn't have in the early 1980's. Seeing as many tropers these days weren't even born by 1988, the Internet gives you the ability to look up many of the events and technology covered in the book.
Jeff is 43 in 1988, meaning he was born in 1945.
All told, Jeff was 202 years old at the end of his replaying - that's the equivalent of living from his birth year of 1945 to 2147. He had ten replays totaling 159 years.
The "skew" is small until his fifth replay, when he is a full year off (leaving 24 years). The next three replays are 4 years shorter (a 20-year replay), 8 years (a 12-year replay), and 9 years (a 3-year replay).
If Jeff is still alive by the 2017 date in the epilogue, then he would be 72 (227, factoring in his replays).
This page was created in December of 2011 - a mere six years short of the replay date of the man in the epilogue.