An initial look at the authorized vs. struck vs. melted numbers for the Roanoke Colony Memorial Half Dollar reveal that >40% of the total coins struck were returned for melting, but, from a different perspective, it can be argued that 84% of the struck coins were returned to be melted. Very different numbers for a coin of two orders.
As I note at the start of many of these "Melting Pot" posts, I've written multiple times about the subject coin(s) - this time the Roanoke Colony Memorial - and prefer not to repeat too much of those previous posts here, so check out the links below for my previous posts on the topic coin(s) which provide more detail about the event being commemorated, the coin itself and the involvement of the US Congress that brought about its creation.The Act that authorized the 1937 Roanoke Colony Memorial Half Dollar did not specify a maximum coinage, but did specify a minimum order size of 25,000. The Roanoke Colony Memorial Association of Manteo, NC took a conservative approach with its coin and placed an initial order for just 25,000 half dollars. The Mint struck the coins in January 1937 (25,015 - including 15 for assay).
Sales of coins from the first order proceeded well enough that the Association decided to place a second order of 25,000 coins in June 1937. As the coin's Act set an expiration date of July 1, 1937 for issue of the coin, the Association was faced with a "now or never" scenario regarding ordering more coins. So, it took a chance and proceeded.
Unfortunately for the Association, the commemorative boom was definitely over by mid-1937 and coin sales soon slowed dramatically. The Association subsequently was faced with a large inventory of coins and few sales opportunities. So, rather than dump coins into circulation or make bulk sales to dealers at a discount, it decided to return 21,000 coins (essentially 84% of the second batch) to the Mint to be melted. As a result, the overall 42% "returned/melted" figure can be considered an average of 0% for Batch 1 and 84% for Batch 2 (each batch representing one-half of the total of coins struck).
1937 Roanoke Colony Memorial Half Dollar

For other of my posts about commemorative coins and medals, including other Melting Pot stories, see:
Commems Collection.
For topics about the Roanoke's design elements, see:
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Design Discussions - 1937 Roanoke Colony Memorial