How valid or verifiable is the claim that a sotapanna leads no more than seven lives? Or a once returner returns once?

There is another claim that practicing earnestly for seven days or seven weeks or a maximum of seven years should be enough to attain nibbana.

Whereas as far as I can see, nibbana doesn't seem too common at all. Certainly not the kind of numbers one would expect if it was possible in a few years.

Is there present day evidence for the latter? If there isn't then it also leads me to wonder about the former.

(Note: I'm not saying arahatship or lesser ariya states are impossible, just wondering about the maintainability and significance of the number 7)

What is the learned opinion here?

The Zen approach of nowhere to go, nowhere to arrive seems more commonsensical to the extent that there is nothing to disprove. On the flip side one can be really only wearing out one's cushion in the Zendo, and there'd be no way to verify one's attainment.

How valid or verifiable is the claim that a sotapanna leads no more than seven lives? Or a once returner returns once?

There is another claim that practicing earnestly for seven days or seven weeks or a maximum of seven years should be enough to attain nibbana.

Whereas as far as I can see, nibbana doesn't seem too common at all. Certainly not the kind of numbers one would expect if it was possible in a few years.

Is there present day evidence for the latter? If there isn't then shouldn't it also lead me to wonder about the former?

(Note: I'm not saying arahatship or lesser ariya states are impossible, just not very sure about the maintainability and significance of the number 7)

What is the learned opinion here?

The Zen approach of nowhere to go, nowhere to arrive seems more commonsensical to the extent that there is nothing to disprove. On the flip side one can be really only wearing out one's cushion in the Zendo, and there'd be no way to verify one's attainment.