the underlying samples for these sounds are originally included in the repetition dynamics patches (e.g. perf-rep_cre9_por, ...). The latter are patches where whenever you trigger another repetition you get another dynamics level, so that you start with ppp and after the 9th repetition you end up with fff, or vice versa. The VSL made all the individual dynamic levels (from ppp to fff) individually available as separate patches in the Resource folder of (nearly) each library. We assembled these individual patches into matrices that are playable via velocity (or velocity X-fade) just like the standard portato, staccato and spiccato patches. We made sure that these HD Shorts behave very similarly to the standard versions: their minimum and maximum volumes as well as their velocity dependence are matched (i.e. you get about the same volume for the same Midi velocity), but their velocity resolution is higher (i.e. the gradual change of the sound with velocity is improved). Due to all this you can easily combine them with the standard patches. They generally have a distinct sound and thereby provide a clear alternative to vary the playback or even use both versions unisono. The HD Shorts do not offer automatic alternations (round-robins). Yet, being assembled from repetition (dynamics) samples they blend very well with the normal repetition patches and you can manually switch to them to even get nine distinct alternations.
The HD shorts are integrated into Articulate Presets, which are VI pro presets for each instrument that contain over hundred different matrices covering everything included in the corresponding VSL libraries. Each matrix covers another playing technique, yet these matrices do not consist of individual patches. Many offer "3D-control" and combine all available recorded versions for that playing technique and blend them to allow you to continuously change up to 3 different aspects of the sound.
I hope all this makes it clearer. However, the simplest way to see what this is, how it works and if this is useful for you is simply to download the full-featured demo and play these sounds 😊.
The demo package includes e.g. the "Cellos S" preset which covers all cello samples included in Solo and Chamber Strings 1 & 2. You can e.g. access all playing techniques (listed in the manual) by program change (PC) messages. Although you can surely also use them without this, to fully take advantage of the 3D-control you will need 3 physical controllers (knobs, faders, pedals, ...) that send Continuous Controller (CC) 2, 3 and 20, respectively. CC20 (Cell X-fade) generally always controls the "section size" (in this preset e.g. blending the Solo Cello and the Chamber Cellos). In the likewise included "Violins D" preset covering the Dimension Violas this controller dials the actual number of players and the auto-divisi feature automatically distributes the played notes among the different Dimension players. What the other two controllers do depends on the particular sound. It is likewise listed in the manual, but you can simply check it out what they control. E.g. for the first (sustained) playing technique CC2 controls the attack and CC3 the vibrato intensity. The new HD Shorts are accessed by PC 109-114 and offer the same continuous control as the corresponding SD matrices.
All the best