Well, it's complicated. Here is the deal the way I see it:
If it is 1-52, it was purchased from Embassy (before Starwood took over in about 2001) and therefore it is 1-52. Your unit could be deeded a week in platinum season (like 13) BUT it has no more advantage than one that is week41 because they are all 1-52. If you are looking for a great II trader, grab one of these older units that are "floating" and try to buy one that is deeded into a good week so that when you call Starwood to deposit it into II, they will deposit a great trader for you. Yes, they HAVE to deposit your deeded week as we just learned. One caveat: if you are looking to retro/requal one of these weeks, it is only worth 81,000 SOs no matter what week it is deeded! Yes, even a platinum deeded week will retro only for 81,000 SOs.
If it is a true 3 season unit (sold by Starwood), the mystarcentral for the owner will say 1-21 as the owner's season and it will be deeded into one of these weeks. Only the true platinums will be retro'd as 148,100 SOs. Soooo, if you are NOT looking to retro/requal a unit, it is not important if the unit is 1-52 or true 3 season.
One thing to avoid is a true 3 season unit that is NOT platinum. If you buy a gold or silver deeded week, you are not ever gonna be able to go during the Spring nor will you be able to trade it during that time. So it is WAY better to own a 1-52 deeded into summer or fall rather than a true 3 season deeded into summer or fall.
Overall, your best bet is to find a week that is in the Platinum season in either case, to avoid the confusion of getting stuck with a property you can only visit when it's 110 degrees!
Hope that makes things clear as mud. Katherine