I claim no experience at all. But here is a comment on the subject...
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Posted by SID6FIVE on the TRAINS website
on Tue, Oct 23 2007 5:12 PM

Several months ago the BNSF started using a new track warrant authority form...I don't know all the reasons they made the change...it seemed to take several tries to implement the change system-wide...I remember the changeover date was pushed back a couple of times...as a result, all the old forms in our yard office were dutifully thrown away and replaced with the new forms, only to have to be replaced with new "old" forms when the changeover date was pushed back a month...the old forms used a four-digit number which was coded to the subdivision the warrant was issued on-for example, the Hinckley sub used 8000-series numbers,if I remember correctly...problem being that in times of high traffic levels they could run out of numbers within the day...which required them to keep other number series clear for use-just in case...the new numbering system uses a three-digit code for the subdivision, a dash, and a sequence number,which is just how many warrants have been given out on that subdivision on that day so far...some trips it's well over a hundred by the time we get there...hope this answers your questions...

Don't worry,it's not supposed to make sense...
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I hope that helps.