I do not think this will help you at the windows, but I find it interesting. As far as I can tell, negative numbers associated with the Derby were not even a thing before the year 2001 – that’s when Monarchos won with a negative number and Millennium Wind had a negative number for his Blue Grass coming in. The archives do not go back before 1997, but based on the figures of the Derby winners, it is unlikely to me that there were any negative numbers run in any of the preps before 2001. It seems like something changed significantly for 3YO in 2001 – they ran faster preps than before, Based on TG figures, it was a very strong year.

3YO top for fastest horses in Derby preps:
1997 – 4’s + 5’s
1998 – 3’s + 4’s
1999 – 2’s + 3’s
2000 – 2’s + 3’s
2001 – neg 0 +1’s (more than half the field had a top of 2 or under)
2002 – 0’s + 1’s
2003 – 0’s + 1’s
2004 – neg 3 + neg 1’s (first 2YO negative I noticed with Read The Footnotes)

While the figures have oscillated after 2004 with some years on average being faster than others for the most part the figures seemed to have leveled out.