Apple Begins Allowing 200 Test Devices Per Developer Account
Previously, Apple only allowed developers to register 100 unique UDIDs during the course of a year-long membership, a number that dwindled quickly when attempting to test apps with multiple versions of devices.
Apple's strict policies prevent devices removed from a developer account from freeing up additional UDID slots until an account is renewed, meaning lost, stolen, or sold devices impact available numbers as well.
Apple has not updated its support documentation to reflect the additional device slots, nor has the company sent out an official news bulletin to developers, so it is unclear if the update is a quietly implemented change or if it is limited to specific developers. At this time it appears that developers are receiving access to the additional slots on a rolling basis.