"The Final Regulations make three important clarifications relevant to 'substantial risk of forfeiture' analysis: [1] A substantial risk of forfeiture generally may only be established through a service condition or a condition related to the purpose of the transfer ... [2] In determining whether a substantial risk of forfeiture exists, both [a] the likelihood that a forfeiture condition will occur and [b] the likelihood that the forfeiture condition will be enforced must be taken into consideration. [3] Transfer restrictions on securities (such as lock-up provisions, buyback provisions, blackout periods and limited trading windows insider trading compliance programs) generally do not create a substantial risk of forfeiture[.]"