The first entry is always the pin's source. Overall confidence is a weighted average of how firmly each reference supports the start and end times used above; a reference counts half as much for every 180 days older than the newest.
Happened as dated, per wpcentral.com: "Your membership journey starts here. Keep exploring and earning more as a member. La…"
Microsoft's[3] own Windows Experience Blog, dated 13 May 2014, confirms the Windows Store refresh - the persistent navigation bar and new Collections page the pin describes - rolled out "today", matching the pin's stored 12-14 May 2014 window.
Microsoft's own support article, dated May 13, 2014, corroborates the same Windows[2] 8.1 Store update - the persistent navigation bar, Collections page, and universal-app badges - matching the pin's stored date.
Something missing or wrong? Say it in your own words: a link that backs this pin up, a different start or end date and why, or a fact it lacks or gets wrong. The AI checks it against this pin's sources, searches for better ones, and adds any page that backs you up. The pin's own sources still count most.