>>49572099>dpptPast my area of expertise, but it looks a lot like what they were doing for ex cards a few years earlier.
Can't say for certain when it began, maybe from the start, but as early as Legendary Collection holos were printed onto silvered cardstock like your pic shows. It seems like WotC printed a new layer directly over the silver, while beginning with EX era it was printed on separate sheets that were then stuck to the cardstock. Maybe the surface print sheets (basically stickers) were made from cheaper materials and even more prone to separating by gen 4.
Sadly I no longer have that Wailord ex, so this is the only photo I have that shows it. You can see along the left border where it's beginning to bubble up.
tl;dr looks real to me