According to the Disney website, the only difference between Full and Preferred is cable (and the internet availability that comes with cable). Otherwise, the same verbiage is used (it's rearranged slightly, but every word is reused!). Now that cable has been added to the Full loops, there is nothing definitionally to distinguish the two levels... which leaves Disney the flexibility to put Preferred folks into historically Full loops! I suspect at some point they will revise the definition to say that the Preferred loops are in preferred locations (near the marina) and that Full has the same amenities in more secluded locales.
As for pet designation, 1600 and 1800 are historically pet loops, and 1700 and 1900 are not. I suspect that they are all pet loops now, since I have seen pets in all 4 loops and IIRC there a poop bag dispensers in 1900. That said, one of the nicest aspects of staying in 1800 and 1900 is the peace and quiet. Maybe it was just a quirk, but the times we have stayed in 1800 it was mostly grown-ups, and never a loud dog. I suspect families opts for loops closer to the pool or marina, and left us a nice quiet loop. 1800 and 1900 are well off of the road, so no bus noise. And it is far from the marina, so none of that noise. 1600 and 1700 have sites that back up to the road, so half of those loops are, in my book, undesirable... unless you are a purveyor of inflatable Christmas joy! Or, if easy access to the pool/post is a major factor. The biggest benefit of staying in 1600 is the proximity to the bus stop and the fact that there are two comfort stations accessible from either the front or back of the loop.
Carol, you said 1649? My records say that the loop only has 45 sites... maybe 1639? Did you back up to the road? Were you near the CS that is shared with 1500 loop?
It was a great site though, I remember that much 
