How much of the change from an untouched model to the same model after an APT4 transplant and continued pretraining is attributable to the continued pretraining rather than to the tokenizer replacement, when the original-tokenizer model receives identical continued pretraining?

Qwen2.5-1.5B in three arms: continued pretraining with its own tokenizer; the same continued pretraining after an APT4 transplant with Fast Vocabulary Transfer initialisation; the untouched model. 0.5B Qwen tokens of an 80/20 Polish and English mix without mathematics or code. Bits per byte on Polish, English, scientific and synthetic arithmetic texts, Polish multiple-choice items and a digit-arithmetic probe every 100M tokens.