Retirement status in Wave 4 is problematic. There was an oversight during preparation for Wave 4 that resulted in questions on retirement status contained in the Wave 2 Continuing Person Questionnaire not being reinstated.
The questions were removed in Wave 3 because a more comprehensive set of retirement-related questions were included as part of a retirement module.
Removal of this retirement module for Wave 4 should have been accompanied by the reinstatement of the original retirement questions, but this was overlooked and not rectified until Wave 5.
You can define retirement status based solely on age and labour force status, but to be consistent across waves you would need to apply the same criteria across all waves.
The alternative is to exclude Wave 4 entirely.