When the engineer gets a new computer, are they supposed to uninstall the software from the old computer before installing it on the new one? What if the installation fails (as can and sometimes does happen)? Normal practice, while not strictly legal, is to get the new machine fully working before doing anything to impair the usability of the old one.
To be sure, the unused software should have been uninstalled after the new software was installed, but--especially under Windows--getting rid of unused software seems to be a rare tendency. Part of this, I think, stems from the fact that uninstalling things can cause other things to break, and part of it stems from the fact that many people have no clue of what software they might need.
I don't know what the best solution to these issues is, but having business software that tracks usage might be helpful. If five machines each show that a piece of software has been used solidly for 8 hours a day, and there's only one license, that's a problem. If three machines have a piece of software installed, one of them has it used solidly for 8 hours a day, the second has it used 8 hours a day except for a couple days, and the third has it used only during the days when it wasn't used on the second (because the second computer's motherboard had flaked out), that should not be a problem if there are two licenses for the software (it would obviously be a problem if there were only one).
Of course, the BSA would probably insist that people buy two copies of a piece of software if they're going to look at the screen with two eyes while running it...
... or don't even know what software is installed. Add/Remove Programs in the Control Panel can help here, but it requires diligence in checking for unused software. At least XP now gives you some hints about how often a particular application is used.
I don't know what the best solution to these issues is, but having business software that tracks usage might be helpful.
My company uses a floating license manager for our product. You buy 3 "seats", and the application checks out a license for the duration of your usage. The application itself can be installed on as many PC's as you like. Any 3 people can use it simultaneously, but a 4th will be refused.
It's not optimal (because the license manager client has some problems), but our customers prefer it to having to buy "seats" for only occasional use.