It can certainly be as you say, Jonathan.
My doubt derives from the fact that here I always have about ten specimens free for the house (they are excellent natural insecticides, for me second only to Menemerus semilimbatus in the house) and this allowed me to measure and photograph them in the various stages of their growth.
In Basilicata the specimens of triangulosa about 3mm long are at most sub-adults.
Perhaps in central Europe the species is smaller.
Raf