I had this problem in past, and this time I want to address it. I am front end developer. I mainly convert design (photoshop, illustrations) files to working web-standard code and make them interactive.
Scenario: I have been working on a project where the original source wasn't present and only a mocked image for a desktop web page was available to me. I was told to make everything "Exactly the same", spacing, margins etc. In other words Pixel Perfect.
While in past I had made "Pixel Perfect" websites when provided source files but this time too the files aren't available because of cheap labour or to save money on a Visual Designer (talking from experience), the changes are last minute because 'Mobile Design' wasn't available and while starting the project.
I asked the CEO if he wants me to approach what I used in my last design and he agreed. This is a project from "his partner" and now his partner got hands-on source file after I insisted (again not that project but similar and no mobile layout). So the work is like redoing a lot of work and the source he wants me to follow is something like Wix (automated website builder) which has the horrendous source code done by Ex-Developer.
I understand non-tech people do not understand the work goes and I had much experience in past. How Can I ask my manager politely that I need a source file with all devices layout to start work otherwise it is redoing most of the stuff. I do not want to agitate Manager, nor his partner or the CEO but want to convey my message across because without proper source, I cannot achieve "Pixel Perfect" and it will go in circles of "not exactly what I wanted".