Kline's MNIST drop-8 protocol is a single-task representational drift, not a disjoint sequential-task switch

By the field's own criterion — that catastrophic versus graceful forgetting tracks representational overlap and task structure (claim-representational-overlap-determines-catastrophic-vs-graceful-forgetting) — the classification of Kline's (2025) setup turns on what his methods actually do. They describe a single MLP trained to convergence on the full 10-class MNIST task, then continued on the same task with one class withheld from the sampler: "we removed all digit 8 examples from the training set and continued training our fully-trained MLP for 80 additional epochs." The general procedure sets "one or more class weights set to zero to measure retention and memory decay." All ten output classes and the shared input/feature space persist throughout; only the sampling weight of one class changes.

That is structurally distinct from the protocol that produced the founding catastrophic result. McCloskey & Cohen (1989) moved a network wholesale from one's-addition facts onto disjoint two's-addition facts — a new, non-overlapping mapping (see claim-catastrophic-forgetting-is-a-structure-dependent-regime-not-universal). Kline never switches tasks; he lets one class drift out of the sampling distribution inside an otherwise-stable task. On French's framework this places the drop-8 protocol firmly on the overlapping, shared-structure side — the side the primary literature associates with gradual, not catastrophic, forgetting — which is why the observed curve decays to a floor near 0.18 rather than collapsing to zero (claim-neural-nets-forget-along-human-like-power-law-curve).

The classification rests on the structural fact, not on Kline's account of why the floor sits where it does. He attributes the non-zero floor to feature overlap between 8 and the circular strokes of 6 and 9, but states it "it is hypothesized" — a candidate mechanism for his own data, not something tested by ablation. The setup's regime is settled by its structure; the cause of its particular floor is not (see watch_flag). The spacing dynamics observed on top of this same setup are treated in claim-spacing-effect-emerges-in-gradient-descent-unbidden.