The source that was voted in yesterday is set up for the contest beginning 15 August 2025, so 1 year 2 months 11 days in advance.
Searching for old contests that had a source you submitted is tricky.
Option 1 - the "submit originals" page has a list of the approved sources you submitted with the name of the contest, try searching for the name in the search box, or google "source name" site:photoshopcontest.com
Option 2 - dig through the archives manually
https://photoshopcontest.com/archives/photoshop-contests.html
Each page will show 16 contests only, the links on the bottom move you to the next 16
https://photoshopcontest.com/archives/16/photoshop-contests.html
https://photoshopcontest.com/archives/32/photoshop-contests.html
When you reach page 40 the count is 624, so about two years back
https://photoshopcontest.com/archives/624/photoshop-contests.html
To go further back, type increasing numbers after /archives/ in the address. Typically add 16 each time, but any other number works. You don't need the string /photoshop-contests.html after the number, so these also work
https://photoshopcontest.com/archives/640
https://photoshopcontest.com/archives/656
https://photoshopcontest.com/archives/672
https://photoshopcontest.com/archives/688
https://photoshopcontest.com/archives/704
To make this more 'automatic' use Excel to create a list of URLs adding 16 to each line, and use a browser extension that can open multiple URLs in separate tabs. I use "Open Multiple URLs" extension for Firefox, there are many similar for both Chrome and Firefox.