I think he addresses that issue specifically in his book. If you
go to his website he has a sample data set to download which has
several years worth of Milford data available so I'd imagine that
his data set was sufficiently large to get around that problem.
After I first bought his book I was disappointed at the lack of
actual source code available so I e-mailed Prof. Skiena and he
very nicely sent me a copy of his simulation code as well as made
it available on his web site. The code was the source for the
actual game simulations but did not include code for downloading
and parsing results/entries and creating player % probabilities.
I had trouble at first getting his simulation code to compile
and run so I printed it all out and translated it from C to Java (language
I know best) and got that to work. I then created from scratch
my own program to do the entry/result parsing and player % probs.
The results have been relatively mixed so far. I have been slowly
but steadily building up my archive of entries/results so hopefully
at some point I can make a stronger determination of what changes
I think I should make to the system.
For now, I have taken some of Skiena's advice and tailored it
towards methods of predicting greyhound races which, in the short
term, so far seems to be doing pretty well. What is not doing
well, it would seem, is the plainfield trifecta pools !! This
past saturday I was at Mohegan race book and hit a tri-box at
plainfield. Whoo-hoo!! Then the amounts posted and I won fricking
35 bucks. 
Not to extend this post to far astray from the topic at hand but,
in general, the pools need some rejuvenation at many venues. The
exacta and tri pools at Miami always seem decent and the payouts
usually make for a happy trip to the ticket window. Looking at
the pools vs payouts at many of the tracks though and it seems
obvious to me that there are a lot of people getting in the money.
That is, a lot of people who know how to handicap a race vs the
people just out to place a few wagers and have a couple of drinks.
Damnit!! We need more suckers at the frontons and tracks!! 
Although at Mohegan race book this past saturday I recall two
amusing situations. The first was a guy who appeared to be drunk
as a skunk staggering towards the cashier and asking her, "What
do I do ? Just pick numbers? Can you explain this to me?"
Taken aback the cashier explained that he could bet on several
different tracks and at those tracks there were several races
available and he could make his choice based on the big screens
all over the room, yada, yada, yada". With a few tracks
closing in on post time I think about a dozen people wated to
fricking kill him for tying up the line. The second thing was
this guy who urgently ran up to the cashier and said,"Gimme
the very next dog track with a trifecta and gimme the 4-5-6 tri-box."
wtf?
Made me think, what we really need is a pari-mutuel "quick
pick". That should fatten the pools and keep certain people
happily ignorant of whatthey are actually betting on.
