Too many things would have to change
Every table that deals with order info uses ordernum as the foreign key. Every page that queries any of these tables would have to incorporate logic that says, "if it's less than 5000 then call it 5000a, unless you really mean 5000." And that would only buy us another couple of weeks anyway. Testing alone for the changes would take longer than that.
And that doesn't account for the fact that until we are completely off of the old system everything we do has to migrate to and from that system. Which is maintained by a contractor on an as-needed basis.
Any attempts to re-use low numbers amounts to trying to crash your plane in a valley instead of on a peak because you'll have a little while longer before you hit the ground. This plane is running on fumes, and we have to switch to the new plane before it hits the ground.
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Microsoft offers them the one thing most business people will pay any price for - the ability to say "we had no choice - everyone's doing it that way." -- [link|http://z.iwethey.org/forums/render/content/show?contentid=38978|Andrew Grygus]