You will notice perhaps there is now a 25% discount - for everyone.
The current 25% discount will be greater than the discount offered to LR3 tutorial owners, so your best bet for saving money is to place your order now.
Current owners of the previous Lightroom tutorials will be given a discount (15%) - but only after the LR4 tutorial is complete in June.
The current 25% (incomplete) discount is the lowest price that the complete LR4 tutorial will have, whether or not you are a previous customer.
There will only be one discount at a time with no overlapping discounts or no 'discounts on discounts'.