When examining trademark applications, the United States Patent and Trademark Office (USPTO) considers whether the applied-for mark is confusingly similar to any registered or prior-filed marks by applying the following thirteen factor-test established in In re E.I. DuPont DeNemours & Co., 476 F.2d 1357, 1361 (CCPA 1973):

1. The similarity or dissimilarity of the marks in their entireties as to appearance, sound, connotation, and commercial impression.
2. The similarity or dissimilarity and nature of the goods or services as described in an application or registration, or in connection with which a prior mark is in use.
3. The similarity or dissimilarity of established, likely-to-continue trade channels.
4. The conditions under which and buyers to whom sales are made, i.e. 'impulse' vs. careful, sophisticated purchasing.
5. The fame of the prior mark (sales, advertising, length of use).
6. The number and nature of similar marks in use on similar goods.  
7. The nature and extent of any actual confusion.  
8. The length of time during and conditions under which there has been concurrent use without evidence of actual confusion.  
9. The variety of goods on which a mark is or is not used (house mark, 'family' mark, product mark).  
10. The market interface between applicant and the owner of a prior mark. . . .  
11. The extent to which applicant has a right to exclude others from use of its mark on its goods.  
12. The extent of potential confusion, i.e., whether de minimis or substantial.  
13. Any other established fact probative of the effect of use. 

If the USPTO determines that the similarities of the marks, the covered goods/services, the channels of trade, and the targeted customers overlap sufficiently, it will issue a preliminary refusal of registration. However, at the time of examination, the record typically contains no evidence that would cause the USPTO to consider other factors in support of registration. It is up to the applicant to provide this information in its response.  These arguments and evidence should address as many of the 13 factors as possible, including the overall differences in the marks, any dominant terms or features in the marks, the exact nature of the goods and/or services, the channels of trade or industries, the conditions under which buyers purchase the respective goods, and any other established fact probative of the effect of use – the 13^th factor.
 
Just in time for Halloween, the 13^th factor becomes a more useful and even a “lucky” tool for applicants who own prior registration(s) similar to a cited mark.  As of today, October 31, 2018, the USPTO’s Trademark Manual of Examining Procedure (TMEP) will be amended to clarify that, when determining whether to refuse registration of an applicant’s mark on the ground of likelihood of confusion with a registered mark, Examining Attorneys should also carefully consider:

1. whether [an] applicant’s prior-registered mark is the same as the applied-for mark or is otherwise not meaningfully different; 
2. whether the identifications of goods and/or services in the application and applicant’s prior registration are identical or identical in part; and
3. the length of time the applicant’s prior registration has coexisted with the registration being considered as the basis for the likelihood of confusion refusal.

Previously, TMEP Section 1207.01 stated that the decision to issue a likelihood of confusion refusal based on a prior registration had to be weighed against the coexistence of the cited owner’s registration and the applicant’s registration as long as the applicant’s prior registration has coexisted with the other registration for at least five years. As of this morning the new TMEP guidelines do away with the specific five year coexistence requirement. Instead, any duration of coexistence should be considered along with all other relevant factors.

The update to the USPTO’s consideration of coexistence reflects both the realities of today’s market in which the confluence of technologies means that more goods/services overlap, while recognizing that brands that have long coexisted in their respective spaces may continue to do so even as their offerings evolve.

In other words, the 13^th factor may become "lucky" for applicants wrestling with how to demonstrate marketplace realities to the USPTO, so applicants should consider claiming ownership of prior registrations at the time of filing.