If you backup company data with sage line 50 v 12, can version 11 use it?

Answer 1

Definitely not with a backup.

There is a version we accountants use called client manager.
There is a wizard in the client's program that exports the data to an email.
When the accountant gets it they can post adjustments and then send the data back.
The clever bit is that the client continue posting data and what the accountant sends to them just updates the data rather than overwriting it.
It also lets the accountant use version 13 or 12 and still post data back to version 11.

Answer 2

I don't think it is backwards compatible.