I believe you can access bills more than 5 years old.
When I was in a chat with a sales representative, I told her to pull up the bill in 2015 to verify something for me.
The back bills online are 18 months. I have read online via google any invoices over that time span can be gotten via a call to Verizon. Hey five years maybe possible.
but don’t believe what any customer service rep tells you unless you can see it in black and white. Verizon oft times doesn’t give the same answers based on to whom you speak to.
I mean, to be the safest, you can print a copy of your bill and gather it with many other bills to be stored in a file cabinet. Maybe put the cabinet in a climate-controlled room... I don't think that's necessary.
One time I cannot find a receipt, or legally a proof of purchase, to receive warranty services. I went back to the vendor for this very purpose to ask a duplication of the receipt. Luckily, they were able to reproduce it.