My two most favourite resources are:
https://cartophilic-info-exch.blogsp...16/06/a-z.html
and
https://www.laststicker.com/
One thing about the Megacracks that seems to get forgotten is to be aware that they are released with updates and editions. For example the Messi rookie is numbered 71 BIS, indicating it's an update. If you ever get the chance at buying sealed product for 04/05 be very careful you are buying the right edition. I believe a similar thing applies to the Panini Este sticker. This year both Kubo and Fati are found in the second edition
https://cartophilic-info-exch.blogsp...-20-02_23.html