You're probably failing to take into consideration length of reign, George IV 10 years, Victoria 63 years. Crowns struck for George IV was for 1821 and 22, Victoria was over 10 years, so in essence there in an over abundance of Victorian crowns compared to George IV. So compare the mintage of crowns, George IV maybe 500,000 in total, Victoria maybe at a guess 4 million for the older head Crowns