The Publisher Resources page has a bit where they tell you the badge ranking criteria.They DID change the criteria a year-plus ago so that an item must have sold for at least $.2 (20 cents USD) to count as a "sale" for the purposes of earning a badge. The change was retroactive, so a bunch of products that had earned medals due to extremely low pricing lost them.
Common wisdom says anticipate earning a badge once you have exceeded its minimum sale count by 5-10%. That's held true in my experience and tracks pretty well with your own estimates above.
The thresholds are the same for DTRPG and DMSGuild, and it no longer matters which platform you check out on to earn them.
For example, if a customer adds an item on DTRPG to their cart then goes to DMSGuild, adds more items, then checks out (or vice versa), the sales still count. It used to be that a customer had to check out on DMSGuild for the sale to count toward a DMSGuild badge, and the same for DTRPG, but they changed that around the same time they instituted the 20-cent minimum rule.
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