HTTP Referer not always being passed

Question

I have an application which records users visits. None of these visits are directly accessed, 100% of these visits are referred from another site.

I am passing

Answer 1

If a user visits your site directly, there is no referrer. It's also possible they have set it up so their browser never sends the referrer.

According to this answer, browsers do not necessarily send a referrer when doing a meta refresh.