I thought they did them at specific times of the year, like they always do half-price membership around Thanksgiving iirc, and i thought the other was March, and i have an email from this time last year saying it ends 31s March (and the common 'fancy that, its been extended' email), but checking my purchase history i bought one on Aug 22nd (2014) so i guess maybe that event isnt as predictable.
I bought a load of content at 2x 6 & 1x 3 items, yet the $100 for $75 is still sitting on my inactive account. Typical really.
Seems like people have been waiting a year for it! https://www.reddit.com/r/iRacing/comments/470p6i/100_for_75_when/