I take it they mean if for example you were to assign yourself 30A and 30B is already assigned to another passenger, 30B isn't going to be turfed out to accommodate a blocked seat for you.

On the otherhand if 30B is vacant at the point you assign yourself 30A then theoretically it should subsequently show to others with lesser status as being greyed out on the seat map moving forward.

Yes it does matter that you're still Silver as the block won't necessarily protect 30B from being assigned until you move up the status ladder. If it were me I'd wait until you reach Gold before assigning the seat you want.

Keep in mind of course the theoretical seating block can be lifted at any time based upon load factors of your booked flight in the event 30B is needed by another passenger.

For additional context, theoretic seating blocks aren't seen by crew on board. For all intent and purpose, it shows on the crew iPads as an open seat so 30B would still be seen as free for the purpose of reseating other passengers if they needed to, even if the theoretical block had protected it from being assigned up until the point that boarding had been completed.

The only way to absolutely guarantee 30B remains blocked and yours would be to purchase it as a comfort seat.