Are you sure they test it correctly- or even fully?
Being in the fire service myself i know that all our cylinders (Hampshire fire and rescue) as in our breathing apparatus (same test standard as full wrap cylinders) cylinders are sent to an outside agency to be tested. Extinguisher cylinders are not tested in the same way- they have a visual inspection after they have been discharged, or after 5 years.
Thats not saying that whatever brigade you took it too doesn't do it's own in house testing but i would be extremely surprised if they could do this on station.
I would check, and even if it has been properly tested, if you haven't got a new label on it showing that it was tested correctly you still won't be able to use it.
My Advice if you've got a cylinder and it needs testing don't take the chance- take it/send it to HPAC or an approved test center.
A.B