Another Serial # question

I have aquired a 1&7/8 blue model 36 and the SN on the butt is AVP 1558.It is marked model 36 on the crane hinge, no dash.Square butt.Flat square cylinder release, old model.Does not appear to be pinned.3 screws on the side plate. No trigger gaurd screw.Production #s 15536 on the crane andport sideof the grip frame.Also on the starbord side of the grip fram is the no. 4787.The grips are SILE oversize replacements.I have read all the sites and am totaly befudled. What year was this made ?