Do we believe that the customer has indeed signed up for that promotion when they registered? It appears to me that NO discounts are being applied at all. The case where they believe 41.9 % discount is being applied is in fact prorating since the VM is a monthly VM being charged for 1/14 – 1/31 (rather than 1/1).

Re: The specific questions asked:
# Regular customer promotions (ie those not tied to trials) are per billing period only at this time. One cannot give a 15 day promotion for regular trials.
# Current limitation is that regular customers can sign up for a promotion only during registration time.

Given the above 2 items, the first part does not apply (ie does it apply only to services signed up after the promo started. since the promo started from the very beginning, all services are signed up by definition after the promo started)

Assuming the customer sign up for a promo, then for
Q a)
a) we would charge $744/2
b) $30/2
c) $30/2

Q b) Yes
Q c) n/a

Re: your last question, here is a copy/paste from another conversation that might be useful:
Finally so I can explain the difference between a promotion and an account discount, they key differences between these are that promotions have to be added during initial signup and usually have a duration, discounts can be applied to the account after signup – but both discount all services they purchase by the discount % (or in the case of promotions you could also just offer a fixed amount off) – is this correct?

# You sort of mentioned it but just to make it clear. Account level discounts have no duration and are applied as long as the discount is active *on the day of invoicing*.