When filing for a trademark, it is important to remember that you are filing for the mark as you use or plan to use it. That is, you can only file for one mark per application. For example, if you have a stylized trademark where you have one word stacked over another, while the other version has the words side by side, although the marks share identical wording, the USPTO will consider that to be two different and distinct trademarks. The same situation applies for word marks - applying for the mark TRADEMARK in one application versus use of the term TRADE MARK will be considered two separate marks.
Keeping that in mind, some applicants may try to file a trademark application where most of the mark remains consistent, but includes a changeable element. For example, an applicant may file an application for the mark TRADEMARK 19, in an effort to secure trademark protection when they use the trademark as TRADEMARK 1985 or TRADEMARK 1999. When you file for a trademark but actually use that mark with changeable element as discussed above, you may have filed an application for something called a "phantom mark."
Aside from certain scenarios, a phantom mark is not registrable. Namely, U.S. trademark law prohibits the registration of more than one mark in an application. That is, if the mark in your trademark application can function as two or more marks, it is possible that the USPTO would reject the application on that basis. These types of rejections occur when an applicant files a statement of use or specimen which shows the mark being used with the changeable element(s). Phantom elements in marks generally involve a date (usually a year), a geographic location, or a model number that is subject to change.
Remember that the primary purpose of registration is to provide notice to potential users of the same or a confusingly similar mark, and that to serve this purpose, the mark, as registered, must accurately reflect the way it is used in commerce so that someone who searches the registers of the USPTO for the mark, or a similar mark, will locate the registered mark. As such, when seeking to apply for a trademark, it is imperative that you file that application for a mark as a whole without any changeable elements. Including changeable elements in an applied-for trademark can counter the basic trademark rule that an application must be limited to only one mark.