Uh, ok. Let's compare production numbers for Demon's to '71 and '72 Dusters.
1971 Demon
Fastback Coupe: 69,861
340 Fastback Coupe: 10,098
Total 1971 Demons: 79,959
1972 Demon
Fastback Coupe: 39,880
U.S 340 Fastback Coupe: 8,700
Total 1972 Demons: 48,580
1971 Duster
Fastback Coupe: 173,592
340 Fastback Coupe: 12,886
Total 1971 Dusters: 186,478
1972 Duster
Fastback Coupe: 212,321
340 Fastback Coupe: 15,681
Total 1972 Dusters: 228,002
Seems like they made an extra 106,519 Duster's in '71 compared to Demons. And, in '72 that would be 179,422 more Dusters. That doesn't even figure in '70 Dusters, of which there were 217,192. Oh, let's not forget '73-'76. That's another 701,164 Dusters. So, grand total
1970-1976 Dusters : 1,332,366
1971-1972 Demons : 128,539
They also made 13,796 1970 Challenger R/T's, so, a '71 Demon 340 is actually more rare than a '70 Challenger R/T. But see how those prices work out.