The service life of the devices was known up-front. You can check for yourself the service life dates of every Chrome OS machine here:

https://support.google.com/chrome/a/answer/6220366?hl=en

The correct deployment strategy would be to make a big purchase at the front end of a device's lifecycle and then only replacements from then on out so that you get the most out of every machine. Future capital purchases would be with a new device and termination date.