Did each developer do a large enough mix of AI/non-AI tasks, in varying orders, that you have any hints in your data whether the "AI penalty" grew or shrunk over time?
TLDR: over the first 8 issues, developers do not appear to get majorly less slowed down.
[1] https://metr.org/Early_2025_AI_Experienced_OS_Devs_Study.pdf
But: if all developers did 136 AI-assisted issues, why only analyze excluding the 1st 8, rather than, say, the first 68 (half)?