As Randy aluded to, there are some certification bodies that sometimes perform part of the Stage 1 off site. Stage 1 cannot be completed until an auditor is on site to confirm that the activties there match the documents including the scope statement. Performing part of the Stage 1 off site saves the auditee the expense of transporting an auditor on site, simply to confirm that the documentation matches the site. That can be confirmed prior to Stage 2 after arriving on site for Stage 2 before starting Stage 2. I have done Stage 1 audits both off site and on site. Off site Stage 1 audits are often only a half day.
However, that has no bearing on a CB confirming that the documents exist before committing to a Stage 1 audit. It is a seperate issue.

Document review offsite prior to stage 1 - Understand
stage 1 offsite - I do not understand still
You say this:
Stage 1 cannot be completed until an auditor is on site to confirm that the activties there match the documents including the scope statement.
and this:
I have done Stage 1 audits both off site and on site
What exactly is this:
That can be confirmed prior to Stage 2 after arriving on site for Stage 2 before starting Stage 2.
??
CB's before were doing a Prep audit (onsite) to check readiness at a cost before Cert audit (onsite). This was optional for customers.
Customers avoided Prep audit for saving money and Cert audit threw up surprises, awkward surprises.
The Cert audit has been then split to Stage 1 + Stage 2. (both onsite)
So prior to stage 1, CB asking for documents and customer providing the same is CB and company convenience, and a small part of the stage 1. Not the stage 1 itself.
I have done Stage 1 audits both off site and on site. Off site Stage 1 audits are often only a half day.
Offsite How... ? By document review and then back and forth with customer.
What if docs say validation is excluded and they have processes requiring validation, which the other docs do not expose?
What if they say the headcount is 15 and the site has 50. People on work effecting quality are contract labor and the company say they do not count them. How is the readiness assessed offsite ?
There are many more readiness issues when I mention awkward surprises ~~~