Is balfourii difficult to grow from seed?

One month ago, I planted 12 balfourii seeds (purchased from Hortus Botanicus) in 2 pony packs, which were placed in a flat with walleriana hybrids. I covered the flat with a humidity dome and placed it on a heat mat (set to 75 degrees). These steps comply with the directions given on the packets for kinds of seeds.

After two weeks, many of the walleriana had germinated, so I took the flat off the heat mat (to make room for other seeds). Those that had sprouted have contined to grow, and others have since germinated. However, the bafourii still have not shown any signs of life.

Any clues to what I'm doing wrong? Do these seeds take longer than 30 days to germinate? Do they need more or less heat, light, or anything else?

Also, should I try to salvage those balfourii seeds I've already sown, or should I start over with new ones?

Thanks!