Excel is a great way of handling big datasets, but beware of this problem: This software autocorrects some of the gene symbols into dates. Without having a gene description column on your datasheet, these conversions are irreversible as there is no way to recover the gene name based on dates.
One way to circumvent this issue is to always open a blank excel sheet and open the .txt or .csv file from “File -> Open.” At the last step (step 3; see figure at top), you have to assign the appropriate columns as text (see figure on top). If your gene name is not at the first column, you will have to manually click on the column with your gene names.
If you have accidentally forgotten to open your excel file in this manner, the other option is to assign the gene symbol based on the gene description. To do this, sort your gene symbols in ascending, which will quickly identify the gene names that are converted to dates. Then, format your entire column as text. Finally, based on the table below, assign the gene symbol back to the correct one.