Pressing 4 and k influence statistics differently - this wasn’t obvious to me.
Marking a word as “4” means the main words known counter increases. In the statistics for a lesson, the word is still counted as a yellow LingQ which I did not expect.
Marking the word as “k” makes it count as a known word in the main statistic and counts it as a known word not a yellow word in the lesson statistic (shown when you click the thumbnail or hover over the bar when within a lesson).
This makes the % of unknown words compared to known words clearer as you can quickly estimate it by comparing few numbers.
I had 900 words marked as 4 and have moved them all to k as it’s more useful.
A word becomes known when it moves from status 3 to status 4. The green check only means it will no longer be added to your Daily LingQs.