Bearcat F8F,
The reasoning behind BA's request to do more tests is to ensure everyone is measured on an even playing field. The 3 flying schools have tended to do their own 'in-house' testing which broadly corresponds do their ab-initio full time course they offer to white tail cadets. For example, I know PILAPT is different from COMPASS (even though the aim of the systems is to measure similar characteristics of people).
Also, the tests may be slightly harder. Remember, they'll be 100 people from each of the 3 schools so it will the creme-de-la-creme so to speak. BA will need a robust set of tests to ensure everyone can be graded fairly but that they'll be a broad spectrum of results on the day so it makes picking the final 70 odd slightly easier.
Here's hoping I'm in the final lot (fingers crossed!). Good luck to everyone else as well.