Once you have your actual documentation certificate, and the center is taking 5-6 months, you will receive an annual notice to renew letter from the Documentation Center. Comes about 30 days before the renewal date. You sign it indicating you still own the boat, and within the month, the Documentation Center sends you the certificate.
Of course, if you are sailing this could pose a problem, so you need to make arrangements for mail forwarding if underway near the anniversary of the expiration of your documentation. The expiration date is on the lower left side of the document.
Some states do require state registration
regardless of USCG documentation; other states make it option, and at least VA says one cannot be both documented and registered. Most lenders favor if not require documentation. Easier to keep track of liens.