Are you talking about this:

Indeed, not to mention of course that in School Hard, Spike is said to
be "just over two hundred". From a Watcher compiled book, that took
great pains to get his human name "William the Bloody", which was
apparently just a nickname given to him by some posh dipshits because he
was so bad a poet. Which incidentally would make him older than
Drusilla. Here he's suddenly barely over a hundred and Drusilla sired
him. You should guess that if they managed to get that nickname given to
him by a lot of digging, they'd realize they were looking in the wrong
century for the nickname.

Anyway, apparently, those posh dipshits like to say they rather get
railroad spikes rammed through their brains instead of listening to
William's poetry. Hmm, usually when someone makes such claims, the event
you rather have happen, is unlikely, but usually actually possible.
What's the point in claiming something rather happens to you, if it
can't happen? That's like saying; I rather go flying than cycling, and
unless you're Superman that doesn't make much sense. So it seems that
either there have been accidents where workers got spiked with railroad
spikes through the thread (seems unlikely to me), or someone has been
torturing people with railroad spikes.

Wonder who that was... well, actually, we kinda know, don't we?
Especially since the book identified Spike as the railroad spike
torturer, and they bothered to name him "William the Bloody". Why would
you identify him by "William the Bloody" if it's just his poetry that
got him that name? Wouldn't you just call him William
Whateverhislastnameis? The only reason why you identify a human before
demon vampire by the name "William the Bloody" is if HE is that railroad
spike killer. Not the vampire, the human.

Which was originally of course the implication why he went 2 for 2 (at
least) with Slayers; he was already a powerful, deadly fighter, and
super dangerous serial killer that got amped up by a vampire demon.

Interestingly; his statement to Angelus: "Have you forgotten what you do
with Slayers? You kill them." heavily implies that BOTH HE AND ANGELUS,
have killed quite a few more Slayers than just 2, the one who wrote the
book just didn't know of it and/or there were Slayer kills after the
book was written. Given how old the book was that Giles read from;
that's pretty possible, of course now it's JUST the two kills, and one
of them in 1978 LONG after the book was written that Giles read Spike's
abbreviated history from.

Actually I think that is a really clever and original attempt to reconcile the various inconsistencies in canon. He's obviously not going to find many takers, but you have to admire his invention. It's amazing what people will come up with.