Each of my 5 timeshares have a week listed on the deed, but that is just for accounting purposes and the week is actually floating. I own 4 timeshare in Palm Desert (1 Shadow Ridge, 2 DSV-2 and 1 DSV-1), and all of them are floating weeks and show a specific week on the deed.
But what is important is the link between the week and the season. Working from memory, I think that weeks 22-26 and 36 to 49 are "white" weeks at DSV1 and DSV2. This isn't the highest season, which is 1-21 and (possibly) 50 and 51? is the Red (highest demand). The lowest at DSV1/2 is Blue and is 27-35. The Blue seasons are often given away or sold at very low prices. The Red weeks at DSV1 and 2 probably could command $2500 to 3500. White weeks? Maybe $1k to 2500. Just a guess.
So look at the week shown on the deed and see which season it is in. Maybe it has value and maybe not.
If your FIL owns at Shadow Ridge (you didn't specify) they have a different season system IIRC. So in that case state what your FIL owns and someone will opine.