verbal warning and paperwork

I work for a Wal-Mart in Kansas, third shift, as a General Merchandise (GM) stocker. One year and four months ago I transferred from maintenance to overnight stocker. At the time, the transfer was done entirely on the training/personnel computer, with me typing in my name, SSN and password, and clicking ‘I acknowledge’ on the screen. I asked if there was anything for me to sign, and was told by the personnel officer that everything is done on the computer, and no hardcopy is needed. I asked for, and received a printout of the document showing my transfer. At the beginning of this year, I was called to the assistant manager’s office, and given a written warning for my performance, which was done entirely on computer, with me typing in my name, SSN and password. I requested a hardcopy and received one. I never signed or dated the documents, although the documents carry a date. At the time, I told the assistant manager that I’d never received a verbal warning, but was assured that I had, though they failed to show the verbal warning on the screen, nor printout a copy. Three weeks later, I am advised that on reviewing my personnel file, the personnel officer had discovered that my file did NOT contain a hardcopy of my transfer from one year and four months ago and the personnel office had printed out a copy, which I needed to sign. As I was already off the clock, I was told to comeback another day to complete the form. This was the same personnel officer who one year and four months ago had assured me no hardcopy with signature was needed. At a previous employer from several years ago, all documents, including transfers, verbal, written, and termination papers where done hardcopy, with ink signatures and dating of signatures done by all parties involved.

Several questions: Is a verbal warning supposed to be documented, with signatures, or can it be merely noted in the employees file by management that a verbal was given? Is the use of only electronic forms allowed by Federal/Kansas state labor law or is a hardcopy with signature still required? If I was never notified of the verbal warning, but somehow the electronic form was completed without my knowledge/consent (assuming this could be proved), would this invalidate the written warning? If they should produce printed documents now of the verbal/written warnings, am I legally required to sign the documents? If I sign the transfer document, which now exist should I date it the day I actually sign it or backdate to the time it was suppose to be done? If I do the latter, am I committing a crime by falsifying the date of my signature to the past date of over a year ago?

Thank you for any information provided.