B737-900 Maintenance Technician reported flight crew O2 bottle installed incorrectly.

Narrative

On Day 0; I was working with two other technicians on an aircraft at ZZZ Hangar. During our scheduled checks; it was found that the crew oxygen pressure was below the airline-required 1000 PSI. A non-routine log page was opened by me; and I removed the bottle from the aircraft. Myself and one of my teammates brought the bottle to a bottle servicing room; and serviced it to full; as normal. Upon returning to the aircraft; my teammate elected to perform the install; and I would perform the operational checks in the flight deck when he was finished. We did this; and I found the checks satisfactory. I proceeded to sign the log page off as complete; and we carried on with other work. On Day 11; I was made aware that on Day 2; a log page was initiated at ZZZ1 by a pilot due to excessive oxygen pressure drop during their mask test. Maintenance personnel at ZZZ1 stated they found the bottle not fully open; and released the aircraft back to service after correcting the issue.Suggestion: It is evident to me that a number of failures happened under my control that led to this incident; which I could have prevented. I find it likely that my teammate failed to open the bottle fully; as it was of the older design of knob on certain composite bottles that is very sticky; and can feel fully open when it is not. I will be immediately reviewing company training material on the subject; as it is evident to me that I must have incorrectly or inadequately performed the operational checks to have thought they passed; if this condition was indeed present after our servicing work. As I signed off the task; I must take responsibility for this failure; but I will nonetheless converse with my teammate to let him know this has happened; and recommend he also review our training material. Additionally; moving forward; I will exercise greater care in how I update and sign off work; particularly in regards to cases in which I did not perform the work entirely on my own.