The following issues were discovered during investigation:

1) existing subscriptions are never matched due to an incorrect equals method on Subscription.SubscriptionCompoundId

2) Fetched "active" subscriptions do not match what is pulled from the IT Subscription service - the IT fetch is then filtered to those within a certain window, and those pulled from existing swatch data are limited to those having an end-date after now - these definitions don't match.

Luckily, these only cause inefficiencies in the subscription sync, and don't prevent it from working generally.