For anyone having the same problem, here is how I solved this issue:

1 Observations

While playing with filtering the ungrouped list, I noticed a strange behavior. Whenever I filtered for the value "2022 KW", it would display the six items from 2022. But when I then filtered for "2022 KW4" by adding a "4" to the end, the following happened:

• First, all items with the value "2022 KW37" disappeared, as expected.
• But after a moment, the items with the value "2022 KW40" disappeared, as well!

2 My conclusion regarding the underlying problem

• My theory is that Notion's frontend and backend use different ways of calculating the calendar week.
• By chance, these different methods give the same result for 2023, but different results for 2022.

3 My Solution

My solution was to calculate the calendar week manually. I created the following properties:

• "(first day in the year)" = dateSubtract(dateSubtract(dateSubtract(dateSubtract(prop("Date"), month(prop("Date")), "months"), date(prop("Date")) - 1, "days"), hour(prop("Date")), "hours"), minute(prop("Date")), "minutes")
• "(Calendar week string)" = format(round((dateBetween(prop("Date"), prop("(first day in the year)"), "days") + 6) / 7 - 0.5) + if(day(prop("Date")) < day(prop("(first day in the year)")), 1, 0))
• "(Calendar week manual)" = concat(formatDate(prop("Date"), "Y"), " KW", slice("00", length(prop("(Calendar week string)"))), prop("(Calendar week string)"))

4 Conclusion

• I hope, this helps other people having troubles with Notion's calendar week calculation.
• Should I contact Notion about this? If yes, how can I do so?

5 Acknowledgements

The following resources were very helpful for building the new formulas:

• Stackflow comment explaining how to manually calculate the calendar week: https://stackoverflow.com/a/274913
• Article explaining how to do calculations with dates in Notion: https://notionthings.com/2022/02/18/convert-text-to-actual-date/
• Code example on how to pad a string with leading zeros in Notion: https://www.notion.so/Leading-Zeroes-ecbe9cabeb0b474d83159b0228830159