the year in review streaks are calculated based on observed day (not submit day), as far as i can tell, but they count only verifiable observations:
An observation streak is a period of at least five days when someone got outside and recorded new, verifiable observations every single day. Here we’re showing the longest streaks that began this year or were in progress when these stats were generated (for individual users we’re also including streaks that ended this year).
so while you may have had observations every day since 1 Jan 2020, not every day since then has included a verifiable observation. see https://jumear.github.io/stirfry/iNatAPIv1_observation_histogram.html?interval=day&user_id=kaphn8d&verifiable=true&d1=2020-01-01.
shifting slightly off-topic a second, one thing that looks a little odd to me is that when you hover over each of the little bars that represents a streak in the YIR page, you’ll see the date range and number of days. the number of days looks fine, but the date range seems to be too early by a day. for example, your shortest streak is noted as 9 days from 7 Nov 2021 to 15 Nov 2021, but as far as i can tell the actual range for these verifiable observations is 8 Nov 2021 to 16 Nov 2021. maybe @carrieseltzer or @tiwane can explain the discrepancy?
finally, if you want to to see your streaks, including non-verifiable observations, you could use this 3rd party streak finder here: https://mapsandapps.github.io/inat-streak/.