Welcome to the Matchbox Challenge Car Release List!
I have tried to pair these up as best as I could:
8, 10, 38 Wal-Mart 5, 16, 67 Service Merchandise, Wal-Mart 13, 61, 72 Wal-Mart 41 Kmart, Family Dollar 27, 33, 57 Wal-Mart, Venture Kay-Bee [27&57 w/52 Wal-Mart, TRU] [33 Kmart, AAFES] 17, 44, 75 Bradlees, Target [44,75 Kmart] [75 AAFES] 37, 47, 52 Wal-Mart, Toys R Us, Bradlees [52 w/27&57 Wal-Mart, TRU] [52 Kay-Bee] 49, 68 Caldor, Kay-Bee, Wal-Mart 9 Bradlees, Woolworths [w/42 Toys R Us] 6*, 71 (?) [6 Toys R Us, Farm & Fleet] [6 w/50 Meijer] [71 Target, AAFES] 12 [w/28 Service Merchandise, Hills, Family Toy Warehouse] [w/21&28 Bradlees] 2, 63 Kay-Bee, Wal-Mart 22*, 28* Toys R Us, Kay-Bee [28 w/12 Service Merchandise, Hills, Family Toy Warehouse] [28 w/12&21 Bradlees] 34, 56* Toys R Us, Kay-Bee, Bradlees [34 Target, Kmart] [56 Farm & Fleet] 19, 21 Kay Bee, Service Merchandise [21 Bradlees] 7, 45 [7 w/29 Venture] [7 Wal-mart] [45 Toys R Us, Wal-mart, AAFES] 35 Target, Kmart 15, 31 Wal-Mart, Kay-Bee 42* Kmart [w/9 Toys R Us] 50 (?), Target [w/6 Toys R Us, Farm & Fleet, Meijer] 28 (new wheels) Kmart 29*, 74* (?) [29 w/7 Venture] [29 Wal-mart] [74 Target, Kmart, Wal-Mart] 34 (new wheels)* [w/22,28,56 Kay-Bee] 22 (new wheels) Toys R Us, Kmart 18*, 14* Kmart [14 Wal-mart] [18 Target] [14 w/36 ?] 36* (w/14 ?) 59*, 46* Kmart [59 Target, Wal-Mart] [46 w/73 Wal-Mart] [46 w/43 ?] [46 w/62 ?] [46 w/30,39,62,65 Kay-Bee/Toy Works] 24*, 26* Wal-Mart [24 Walt Disney World] 73 Kmart [w/46 Wal-mart] 43*, 23* [23 w/32 Wal-Mart] [43 w/46 ?] 32* [w/23 Wal-Mart] [w/53 Kay-Bee, Bradlees] 39, 53% Bradlees, Kay-Bee [53 w/32 Kay-Bee, Bradlees] [39 w/30,46,62,65 Kay-Bee/Toy Works] 30 [w/43 Wal-Mart] [w/39,46,62,65 Kay-Bee/Toy Works] 62 (w/46 ?) (w/30,39,46,65 Kay-Bee/Toy Works] 24 (new wheels) (?) 55%, 70% (in Starter Collection only so far (Target, Toys R Us, [55% Wal-Mart])) 65 [w/30,39,46,62 Kay-Bee/Toy Works] 1,11,20,25,54 Kay-Bee, Toys R Us 3,4,40,48,51,58,60,64,66,69 Kay-Bee, Toys R Us* These models have appeared in boxed format.