I wintersowed Wild Geranium (geranium maculatum) and got a 50% germination rate. That was my first attempt at wintersowing and growing geraniums from seed. My other WS efforts have done quite well though.

Yep, I find it can be a bit iffy although I have lots more success growing seeds from my own plants. Geranium sylvaticum, nodosum, soboliferum, platyanthemum, pratense and incana and (obvs) sanguineum and phaem are relatively easy, germinating quickly and gently bumbling along for a year or soGermination rate varies from almost 100% to less than 50%...and quite a lot of seed sellers put a tiny number of seeds in a packet - always makes my heart sink a bit when there are 8, 10 or 12 seeds. I have never tried macrorrhizum because it is such a doddle to nip bits of root off and poke them in the ground, water in, walk away. I have spent many hours rootling through huge geranium clumps, searching for elusive seeds - all those sterile, long flowering types...but sometimes a busy, roving bee comes along... and a few seeds are produced.
Annoyingly, I have zero luck with direct sowing, yet self-seeding volunteers have no lack of vigour. I am planting prolific types to take advantage of this.