I have the Skana Incarnon adapter installed on the Prisma Skana. This has the Guardian's Promise, Orokin Reach, and Elemental Excess perks enabled, Additionally, I have another Prisma Skana without the Incarnon Genesis. Both have the Crimson Dervish stance. The Prisma Skana with the Incarnon adapter is NOT in the Incarnon form. Neither weapon has any other mods on them.
For both weapons, I did the following steps in the Simulacrum:
Equip the weapon.
Spawn a Brood Mother at level 195 (level is likely irrelevant since Brood Mother has no armor)
If Pause AI is enabled on spawn of the Brood Mother, disable Pause AI to remove stealth bonuses, and re-able if you want the Brood Mothers to stay still.
Use the 1st hit of the Neutral combo of Crimson Dervish to hit the back of the Brood Mother.
Repeat the 1st hit of the Neutral combo of Crimson Dervish to ensure the damage number is consistent if necessary.
From the above steps, I found the Prisma Skana without the Incarnon adapter deals 531 when not dealing a critical hit and 1170 when not dealing a critical hit. This makes sense since the 1st hit of the Neutral combo of Crimson Dervish has a 300% multiplier and Prisma Skana has a base damage of 170. 531/170 is about 3.12, which makes sense since the Brood Mother has a weakness of 25% to slash damage. Likewise, since Prisma Skana has a critical multiplier of 2.2, (1170/2.2)/170 is also about 3.13.
I found the Prisma Skana with the Incarnon adapter deals 635 when not dealing a critical hit and 1399 when dealing a critical hit. Guardian Promise has a flat damage bonus of 100. 635/(170+100) is only 2.35, which is much less than the 300% stance multiplier that Crimson Dervish should have. Instead, the equation (635-100)/170 = 3.15 seems to fit better, which means the equation (3.15*170)+100 = 635 is likely true, thus the 100 flat bonus from Guardian's Promise is applying after the stance multiplier. Likewise, for the critical hit, ((170*3.15)+100)*2.2 = 1399 seems to be true, suggesting that the flat bonus applies after stance multiplier but before the critical damage multiplier.