Start with two scope maps
Do not infer a paper from the source book, file name, or an old revision folder. Map each topic and question to the applicable paper using the current official syllabus and keep ambiguous material out until checked.
Measure each paper separately
Track coverage, attempts, delayed retrieval, and recurring errors for each paper. A combined percentage can hide a weak paper or overstate readiness when one side has received much more practice.
Rebalance without abandoning breadth
Give extra sessions to the paper with the clearest repeated gaps, but keep a minimum retrieval cadence for the other paper. Review the split weekly rather than reacting to one difficult set.
Integrate only after separation
Mixed practice is useful once every item is correctly labelled. Preserve the paper label in review queues and error notes so later practice does not erase the distinction.