Several years ago I was invited to two weddings several months apart. I couldn't attend either so I selected the most expensive gifts from their registries - $300 each for big china platters in their pattern. I didn't get a thank you from either, and when I called both to see whether they received their gifts I was not only told no but that I should follow up with the stores. When I did the stores claimed that the gifts they charged my card for were delivered. I had no way to prove otherwise so I let it drop, suspected, probably rightly, that they were each too rude to write thank you notes and too embarrassed that I'd implied it by my followup so they simply LIED. It's just too much of a coincidence that it happened twice.
I consult the gift registry, but I don't always use it. It gives me an idea what they'd like, but I may go elsewhere.
Of course the drawback is that the item, or its counterpart, is not crossed off the list, and somebody might buy them the same thing.
I always take personal delivery of the gift at the store, to confirm the wrapping appearance is what I wanted. And I deliver it myself, to ensure timeliness. There was only 1 exception for a wedding across the country I couldn't attend. And that gift did arrive on time.
I've always gotten a thank-you card. But for my own wedding in 1978 we lost some of the cards with the gifts, when others carried them to my parents' home afterwards, as we began our 3-week honeymoon trip the next morning. I recall there were a few gifts we couldn't identify & acknowledge when we returned. Maybe that happened here.