Hammer Release leverI'm not sure what you are referring to as a number engraved on the separator. If you are referring to the slide, some PP series pistols have a number scratched inside the slide matching the last numbers of the serial number. Theory is to keep the slide with the frame together during construction. Please give a better description of what you have. Photos would help.
https://www.waltherforums.com/forum/attachment.php?attachmentid=88746&stc=1&d=1584294032IMG_5034.jpgIt's kinda complicated. Scroll down WAY down to additional options and to manage attachments. Click on that and go from there...photos have to be attachments. I've only done this twice and I might be leaving something out.