Can a reference add supporting evidence to a letter?

Please can I use only reference letter as an evidence if the referee already attached a few screenshot evidences to the letter? As i no longer work in the company, i dont have access to get dashboard screenshots, but my CTO wrote me a reference letter and i requested he adds screenshots of the admin dashboard for the period i worked in the company. In total his letter is about 3 pages, page 1 is his letter, page 2 and 3 are screenshots of dashboards. Is this fine?

I believe if he could screenshot and put it on the letter, he could as well be able to send you to use for an evidence. Do not put screenshots on letters. Let him send you the screenshots and you create evidence around it.

But won’t he putting it into a signed letterhead carry more weight

Nope. Just attach 3rd party proof for his relation with the company