I believe David mentioned users who had purchased the first shortcut guide might get a discount. Is this still happening? I received an email promoting the Field Guide itself, but it did not mention previous purchasers.
There’s discussion of the upgrade offer in this thread:
It was reconfirmed on MPU Podcast yesterday (September 22) that an email was sent to all previous purchasers. Also, a 5$ off coupon as well for new purchases (too bad I bought it on Saturday - 
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