Shopping Does Volks re-release dolls often?

The Harry Potter dolls are still rather new so I don't think they'll pop up secondhand so soon... (And I don't think anyone has even received them yet?)

Not sure about the other collab dolls, but for Miku they tend to release different versions of her from time to time probably due to her popularity? But there are also lots of other popular character that they haven't rereleased.

Volks doesn't really have a pattern of whether or not they will re-release their collab dolls.

 

Volks will occasionally do Best Selection (Preserved, NIB older dolls for lottery sales), Best of the Bests (older sculpts with new outfits/makeup/etc), on top of sometimes doing new versions. For instance, Lieselotte has had all three of these, having been in Best Selection lotteries, multiple Best of the Bests releases, as well as her recent Galerie de l'esprit release. There's also one-offs, which can include (but are not limited to) old limited sculpts and collabs. Limiteds usually won't be used as one-offs until quite some time after their original release. This is in regards to Super Dollfie.
You also brought up Dollfie Dream, so I'll note that they can also have Best Selection, but instead of Best of the Bests, it's usually reboots or "Version 2" dolls. See: Vocaloid Reboots, Rin Tohsaka UBW Version, Asuna Titania Version, Mirai II, Candy Memorial Edition, etc.
Dollfie Icon is a separate ordeal from both of these, and they essentially only get released once a year in USA and once in Japan. So far they have ALWAYS been lottery sales. If you get into Volks, you'll notice they're very fond of the lottery system. Frustratingly so... Anyway, they're nigh impossible to get outside of USA and Japan, so much like the Harry Pottery dolls, you'll need a proxy service if you don't live in those regions. There's a number of doll hobbyists who offer their services for these cases, I'm sure you could find several in a quick DoA search.
As for the specific dolls you mentioned, I can break down each of those. First and foremost, Miku. She has numerous releases and is one of the few DDs who will come up for sale during events like Magical Mirai, but it's still not easy to purchase her during these times. Her specific doll releases include: DD Hatsune Miku (1st ver), DD Snow Miku (1st Ver), DD Sakura Miku, DD Hatsune Miku Reboot (aka 2nd ver), DD Snow Miku Reboot. Miku is a very beloved Dollfie Dream in particular, so if you're after any DD limiteds, she's the easiest to go for in all honesty. I would not be surprised both regular and yuki reboots are for sale for the 20th anniversary this year.
The trickier one is the Harry Potter dolls. These were Japan-only, you needed a proxy service to preorder them. They're set to arrive this Spring unless something comes up IIRC, so I'd recommend watching YJA, Mandarake and Dollyteria/DOLL UP! during that time if you're after one. These weren't available through Volks USA, probably a licensing thing? So they may be a bit more difficult to get in general.
In regards to the Disney dolls... yeah, no clue honestly, that was a bit unusual for Volks. I'd assume it's another licensing thing, although they weren't up for resale on Volks USA, only JP.
tl;dr Volks doesn't re-release in the same way other companies do. When getting into Volks, forget everything you know they have their own ways of doing things... lol
Oh, and I forgot! This year they're celebrating 25th SD/20th DD anniversary! So there should be some best selection lotteries and the like, potentially clickwar resales of some limiteds as well! It's a bit hard to say as we don't have all the details yet, but keep an eye out if you're after anyone in particular

 

TBH, I don't think they will re-release the Harry Potter dolls. I managed to secure all four through a proxy, but it was hefty price. I’m a diehard HP fan and they became my ultimate grails with combination of my love for HP, BJD, and wanting to own something Volks. Since the collab between HP brand and Volks, and only sold at the Mahodokoro shop, its highly likely they wont be re-released. Expect the value on them to skyrocket insane price the minute they are shipped out. I’m looking forward to having them home soon.

 

there are few proxies, but one allowed me to do layaway plan was Japan Doll Direct. But the fee is very high due to the cost. I ended up paying about $350 fee each time and had to put down nearly 50% first. I got Ron and Hermione right on the very last day it was available and Harry and Snape on last day. Cutting both very close. I still owe a bit left on the last two, I hope Volks does not release any more new harry potter dolls, my wallet needs a break! I would love to get my hand on Draco if they ever release him next.

 

If you're on facebook, I would check out various BJD specific sales groups, I have seen some people already trying to sell their Ron and Hermione, though I haven't seen a Harry or Snape yet.

Some groups to search for are Volks BJD Sales, BJD Lovers - Sales, BJD Sales Universe, and BJD Adoption. There may be others, but those are anti-recast so are safe to search in. As a heads up, most groups ask you to answer questions when joining -- I didn't notice at first and couldn't see some groups for a time, oops.

 

Harry and Snape wont be released until August, which is why they’re not yet on the ebay market yet.