I have read many theories on this and a good number of them seem plausible. I believe the numbers are all bus routes. The biggest problem with definitively proving this theory is that I only have access to current bus routes and not the routes that existed in 1999.
Almost all of the numbers found on the notes are bus numbers in the St Louis area. I suspect that this would probably be true of most areas so I had to make more sense of them before I felt comfortable about this. On one of the pages the number 75 appears. On the other page there are a series of numbers which when taken in order are routes that intersect with the 75 route.
Line 10 on the page labeled NOTES has the numbers 36 74 27(9) and 75.
The 27 could be a 29 although that would not work out with the current bus lines. If looking at the bus system map of the area traveling west - east on the 75 line each of these numbers is a bus route heading south in the order listed above.
I have also noticed some patterns which could be streets individual bus routes take although this will take a good bit more investigation on my part.
One additional item I thought of while writing this post was that what look like the letter k could be a symbol denoting a bus turning. That is wild speculation at this point though.