Private seller on another photo forum. It's well expired. I think I will have to shoot it at 800 or so due to the age.
Maybe even EI 500. Remember, even when fresh, it's not really a 1600 speed film. More like 1150. A lot of the grainy, underexposed results you're seeing online are due to underexposure.
I treat it like ISO 1000 when it's fresh. If it's more than a year out of date, don't expect to be able to get even EI 800 out of it. Fast film ages fast. Some rough guidelines:
Fresh....................................................EI 1000 or maybe 1250
At expiration date....................................EI 800 or maybe 1000
A few months past expiration (frozen)........EI 800
A year past expiration (frozen)..................EI 640
Two years past expiration.........................EI 500
3-4 years..............................................EI 500 or maybe even 400
You could theoretically push process, but the more expired the film is, the less well it tolerates that. I wouldn't bother unless you're after a special effect.