I have a small bottle of the parfum, and I absolutely adore it. But it is always a little bit spoiled for me when I use it because I know when it is finished it is gone forever...
As far as I know, Guerlain did not choose to discontinue it, instead they chose not to reformulate and reissue it so that it would conform to the (relatively) recent EEC regulations on fragrance ingredients. The EDT, having a lower, and therefore 'safe' concentration of whatever it is that has become a problem, can continue to be produced and sold.
I know it is for 'our' safety that these regulations came in. Just for example (and I do not think this particular example applies to Apres L'Ondee) - we were all told (I hope!) when we were young to be careful of perfume and sun exposure, right? That perfume could cause sunburn or skin discolouration if we went in the bright sun after spraying on perfume. Well, it won't anymore. There is now virtually no risk - the fragrance ingredients that can cause photosensitization are limited by law in Europe to such small amounts in a scent that it would be almost impossible. The main photosensitizers in perfumes are in the citruses, particularly bergamot, and nowadays these are fiddled with so that they are safe, and this quite definitely affects their smell. That is why a vintage Shalimar smells so good - all that unrectified bergamot!
On the other hand, if most people are like me, then they will pour a vat of Apres L'Ondee EDT over themselves in the morning, and keep a spare bottle in their bag for frequent redrenching throughout the day! So whatever the toxin, or allergen or whatever, that a small spritz of the extrait would have caused to be slightly over the EEC limit, is instead applied 10-fold by overuse of the EDT.