We bought a set of returns of which one should have been the 6020 piece Hogwarts castle. We received 37 bags that are represented in the pics below packaged neatly in the Hogwarts box. We have bags 1-37 with no instructions and no idea which set they belong to. We might as well build it since it's here. :) Any help would be great.
TLDR. Although bricks seem to be packed in sealed bags, these looks to be a mixture of parts since none of existing set inventories contain such combination of bricks.
More details below.
Based on the colors of the bricks you have received this is definitely not a Hogwarts Castle.
Let's start with contents of bag #36, since it has elements easier to identify. The combination of Door 1 x 4 x 6 with 4 Panes and Stud Handle mentioned in another answer is definitely not in Medium Blue, but some shade of Azure. Checking Bricklink for colors available for this element we can conclude this is Medium Azure colored item. Now this element come in just 5 sets, none of which have Plate, Round 4 x 4 with Hole OR Brick, Round 4 x 4 with Hole in
Dark Tan. So the set this bag comes from doesn't exist.
Now let's see bag #4. Combination of Brick 1 x 2 in Coral color as well as Slope, Curved 2 x 1 x 1 1/3 with Recessed Stud in Lime may suggest this is Bricks and Animals (11011), but it doesn't include any of Slope, Inverted 45 2 x 2 in shades of blue. So no set for this bag as well.
Bag #19 again, suggest combination of Brick, Modified 1 x 1 with Stud on 1 Side in Coral color with Slope, Curved 3 x 1 x 2 with Stud in Lime suggest this may be Bricks and Animals (11011), but this set doesn't contain Plate 4 x 4 in Green.
These bags come from either set that has not been inventoried yet on Bricklink or incorrect bricks have been packaged for particular set (which might explain why they have been returned). The source of these bricks/bags would be some larger set from LEGO Classic series.
Bag 36 contains a Door 1 x 4 x 6 with 4 Panes and Stud Handle (Medium Blue) which was featured in 5 sets.
11003 Bricks and Eyes 10264 Corner Garage 10703 Creative Builder Box 10702 Creative Building Set 11005 Creative Fun 10260 Downtown Diner 31025 Mountain Hut 31065 Park Street Townhouse
41167 Arendelle Castle Village 75958 Beauxbatons' Carriage: Arrival at Hogwarts 11005 Creative Fun 11013 Creative Transparent Bricks 80102 Dragon Dance 71730 Epic Battle Set - Kai vs Skulkin 70674 Fire Fang 41395 Friendship Bus 71043 Hogwarts Castle 76129 Hydro-Man Attack 70668 Jay's Storm Fighter 70667 Kai's Blade Cycle & Zane's Snowmobile 70675 Katana 4x4 70677 Land Bounty 70680 Monastery Training 30534 Ninja Workout polybag 40342 Ninjago 2019 Minifigure Set blister pack 75270 Obi-Wan's Hut 75937 Triceratops Rampage 70840 Welcome to Apocalypseburg! 70419 Wrecked Shrimp Boat 75255 Yoda
These two pieces have only appeared together in 11005 Creative Fun.
11011 Bricks and Animals 10717 Bricks Bricks Bricks 11717 Bricks Bricks Plates 70803 Cloud Cuckoo Palace 10703 Creative Builder Box 10702 Creative Building Set 8961 Crystal Sweeper 45810 FIRST LEGO League (FLL) Jr Challenge 2019 - Boomtown Build Inspire Set 41345 Heartlake City Pet Center 71367 Mario's House & Yoshi - Expansion Set 41339 Mia's Camper Van 60270 Police Brick Box 7676 Republic Attack Gunship 75021 Republic Gunship 21208 Resort Designer 76134 Spider-Man: Doc Ock Diamond Heist 70922 The Joker Manor 41455 Unikingdom Creative Brick Box 60125 Volcano Heavy-lift Helicopter
10717 Bricks Bricks Bricks 11717 Bricks Bricks Plates 10704 Creative Box 41340 Friendship House 41108 Heartlake Food Market 41310 Heartlake Gift Delivery 41253 Lonesome Flats Raft Adventure