A certain developer "...recorded all of the legato samples up to a major 9th" in their brass library, to achieve a more natural legato.
What does it mean to record all of the legato samples? and is this really the best way to achieve a natural legato?
Say you begin with A'' on an instrument.
1.01 - You record the player playing A''-Bb''.
1.02 - You record the transition A''-B''.
1.03 - and so on
1.20 - You record the transition A''-G#''.
1.21 - You record the transition A''-G''.
1.22 - and so on
2. You repeat these steps for any beginning note of the instrument
3. You cut out just the transition phase of all the samples.
4. You write a script or program your sample player in such a way that every time when a legato is played, such a short transition sample is faded in and out between the actual legato notes.
5. Eventually you repeat all these steps recording portamento instead of legato as an additional option.
Something along these lines. A crazy amount of work, but the result can be very effective.
recording a real slur is always going to yield the most realistic legato. That's why no one can touch VSL in my humble opinion. I have tons of libs and like all of them for different things but whenever I'm in need of a legato brass or woodwind, I turn to Vienna SE. Period.