I think that plate and getter design are part of the development of the tubes and the "W" stands for improvement.
Citation from thetubestore.com: "5654W (...) Replaces the 5654 tube or 6AK5-W tube types."
I have not found a file describing how the improvement was conducted. So, I presume that (for Sylvania) black plates and halo getter reflect the best of these tubes in this respect. "W" describes a later tube type in general terms. It is also not clear to me whether the "W" requires the black plates or is just a mechanical durability improvement for example. You could ask the seller which year the tubes are from. I would think they are rather 70s with black plates than 60s.
Alternatively, you could contemplate dbtubes.com to order from a variety of JAN 5654W tubes.
One small information more. When comparing the GE grey plate with the Sylvania black and grey plates, the Sylvania grey plates from 1967 are darker than the GE grey plates. A seller might be tempted to call them black if he has no real black ones around. Unfortunately, I have no camera here, which could visualize the differences.
Short Sylvania JAN 5654 W (1974) vs non W (1967) update after 20 hours of burn in: The "non-W" treble smoothed out.
Edited by Acapella11 - 7/20/12 at 5:16pm