You can only have one current signup at a specific location. There is nothing definitive in the DoD reg on this but the second submission should (usually) overwrite the first and your signup "clock" will restart to coincide with the latest signup date (i.e. retiree signup will be valid for 60 days from the latest signup). If you have to signup twice at the same location then annotate your change of plans in the remarks of your sign up request or in your email. A prudent and savvy Space-A traveler will follow up and contact a Pax Rep to verify the most recent signup was received and has replaced the current one.
What happens if I signup more than once at the same location?