When a gate valve is newly manufactured I can understand why it needs a full pressure test to ensure the integrity of the casting or forging and to proove the pressure containment ability.  If that valve develops a leak because of a bad bonnet gasket or stem seal and the gasket or seal is replaced in the field, would you have to do a full pressure test on the valve or would a test to service or operating pressure be sufficient?  There has been no change to metallurgy, metallic pressure containment parts have not been changed, and no welding has been done to the body.  To remove the valve from the line and send it to be pressure tested could result in a significant shutdown if a spare valve is not available.For some uncritical (in this connection) applications, for instance with non-flammable uncritical, lower pressure water pipelines it is commonly done the easy way, with local smaller testing.
For applications on the other end of the scale, it is equally common to require a full test with the valve out of the rig for testing.
Local and official codes and standards will vary and could also be vague or could be interpreted in different ways.
It all goes down to the local users final analysis and own safety considerations by checking  all existing local codes and establish, after risk analysis, a written quality manual
incorporating the procedure for repairs and testing. You will not get an international quality certification without a procedure for this.
The difficulty is of course as you state finding the correct information and interprete this for your purpose.

MORE NEWS