Although the QI series' were usually stockpiled by recording them in blocks a few months before scheduled first run transmission, so the series gets a nearly uninterrupted consecutive weekly run. As the bulk of the series 18 originally scheduled studio recordings happened to fall at the early 2020 start of the covid-19 pandemic, as with nearly all television studio production being cancelled, it soon becomes apparent that the series production ended up in a widespread stop-start production and schedule chaos, in particular as various lockdown levels affected both production staffing and available guests. This is why the transmission dates are so spread out over the year, with the series only getting to the early teen episodes in January 2021.
Episode 18 (XL version) was finally premiered in the first week of April in 2021, nearly a full year after episode 1 premiered in May 2020. By an unfortunate, or deliberate, scheduling decision, by the UK's Dave channel, known for its endless re-runs of the entire run of QI & QI XL, series 18 was scheduled as "new to Dave", in April with nearly every episode scheduled, one episode a night, monday to thursdays, starting within a week of BBC 2 finishing their premiere run of QI XL season 18.