TN info for Pay change

I have a strange situation. Please help.
I am about to appear for my TN extension. My visa expires in month and half. But 3 months ago, because of the present economic conditions, I had a pay cut of approximately 20%. I recently came to know that if the pay changes, I should get a new TN.
1. Is this going to be a big issue at the POE?
2. Does the officers at the POE has access to our tax records and other important information?
3. Do they keep track of how much pay was mentioned in the last TN offer letter?
4. Lastly, I did not file my taxes yet. I just kept the W2 with me and plan to do it later, if it is going to help me.

Please shed any light which cold be of use to me.
Thanks very much

Although they would like to, USCIS currently doesn't have access to IRS records, including tax returns. They don't know whether or not you have filed a return, or what your income was for the previous year. I assume that USCIS could compel the IRS to hand over records if they wanted to, but they don't readily have access to that information when you are being interviewed at the border.

I recently came to know that if the pay changes, I should get a new TN.

You came to know incorrectly. Pay levels are only relevant on H-1B. Technically you can be in the US on TN-1 and not be paid at all, you could be in a volunteer position (and various people are). How much you are paid doesn't matter on TN-1.