I think at least three factors can be considered:
1) I believe the Canada's 150th Anniversary privy SML has a mintage of 150,000; the Tower Bridge privy SML had a mintage of 75,000. That's a factor of 2X - not small/insignificant! I would expect to see more of the 150th Anniversary SMLs in the market when the mintage disparity is considered.
2) The Tower Bridge privy dates from 2009 vs. the Canada's 150th Anniversary privy SML from 2017. Generally, a more recent coin release will support greater availability. It's not always the case, but more recent dates may not have yet achieved the same level of dispersion within the market, hence greater availability.
3) IIRC, the Tower Bridge SML privy was released over in Europe; the vast majority might still be in Europe vs. North America.
Just my thoughts, your mileage may vary.
1) I believe the Canada's 150th Anniversary privy SML has a mintage of 150,000; the Tower Bridge privy SML had a mintage of 75,000. That's a factor of 2X - not small/insignificant! I would expect to see more of the 150th Anniversary SMLs in the market when the mintage disparity is considered.
2) The Tower Bridge privy dates from 2009 vs. the Canada's 150th Anniversary privy SML from 2017. Generally, a more recent coin release will support greater availability. It's not always the case, but more recent dates may not have yet achieved the same level of dispersion within the market, hence greater availability.
3) IIRC, the Tower Bridge SML privy was released over in Europe; the vast majority might still be in Europe vs. North America.
Just my thoughts, your mileage may vary.
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