A control without evidence is a statement. Evidence is the file, image, or snapshot that shows what was true on a date. It stops being useful when that date is too old.
What to keep
Keep the artefact once, in a library, and point tests at it. That is different from attaching a fresh copy to every email. Give it an expiry when it should be reviewed or retired.
Expired evidence should not be treated as proof that the control is still effective. Missing evidence should not be treated as a pass.
How tests use it
Tests record whether the control worked. The library is where the files live. How ISMSVision helps with evidence is the product.