You can tell an idol's first-week sales by looking at the number of fan signing events

These days, whether it's a major agency or a small one, "pulling forward" sales is so common that the reliability of album sales has decreased compared to the past.
You can consider sales up to the 3rd generation to be truthful, but from the 4th generation onwards, there is a lot of inflation.
Whether it's boy groups or girl groups, they first pull forward sales and then fill the numbers with endless fan signing events.
Since they are technically selling them, it's a strange form of marketing that isn't quite "chart manipulation" (sajaegi) as long as they are actually selling.
This is why the actual scale of overseas tours has been low since the 4th generation.
If fan signings are low but album sales are high: Expect a large tour scale.
If album sales are high but the number of fan signings is also high?: It's easy to understand if you assume the company pulled the numbers forward and the tour scale will be low.