| Loudog,
There is an incredibly variety of different interpretations and performance practices when it comes to Stravinsky's works. There are a few reasons for this, here are the two I think are cause for the most confusion:
1) Different editions. For a variety of reasons (copyright issues, error corrections) there are many different versions of some of Stravinsky's major works. Firebird and Petrouchka come to mind, but are certainly not the only ones. Also, errors in the manuscript and errors in early editions that were never corrected. (The worst as far as trumpets go is a figure in Rite of Spring that STILL is publshed in the wrong transposition).
2) Stravinsky the composer vs. Stravinsky (and Robert Craft) the conductor. Stravinsky conducted his own works frequently throughout his life and left a recorded legacy. The problem with this legacy is that the conductor often varied from the composer's score. This is especially relavent whn looking at tempi (compare Stravinsky's recording of the first movement of his Octet with the printed metronome marking.. YIKES!). This leads to an interesting debate... Was Stravinsky the conductor making definitive choices about the way he wanted his pieces performed, or was he just another conductor who ignored the composers intent?
Now, to answer your question: My guess is that Boulez heard a recording conducted by Stravinsky where the trumpet player slurred it (if its the one I'm thinking of, the trumpeter player didn't even play the written rhythm) and decided that Stravinsky's recording takes precedence over the score. Most ensembles follow the score, as you have noticed.
As far as getting the parts, I can't be of much help, other than to say that if you can get your hands on the newest edition by "Chester Music," that's probably the best way to go. Hope this helps. I'll look around and see if I can find the photo copy of my part that I could scan and email you. No promises though (my "office" is a mess!)
-Jimi
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