Links between mathematical attainment and economic performance, coupled with England's poor showing in international comparisons of skills, have focussed attention on post-16 mathematics education, for example, in the UK Government's 2017 Industrial Strategy. Whilst high-stakes academic qualifications at 16 (GCSE) and 18 (A-level) have stood the test of time, the 'forgotten third' of students in England's Further Education colleges have fared less well. Over the last 30 years a series of mathematics qualifications for vocational students have been established and then discarded. This paper utilises a theory of change approach to understand this repeating pattern for three successive curricula: core, key and functional mathematics. Waves of rise and decline include critical moments of reinforcement, or synergy with wider reforms, but trajectories are also affected by shifting policy visions for Further Education and entrenched knowledge hierarchies that value academic mathematics qualifications over vocational ones. Whether 'alternative' mathematics curricula for FE students can achieve longevity and widespread recognition remains to be seen. The implications from this analysis of historical trajectories are that changes to established attitudes and educational values are needed to halt this repeated cycle of short-lived alternatives to GCSE Mathematics.