The Denver Souvenir sets started in 1972 and ran continuously up to 1998 - I now have 1 from every year.
Getting the Denver sets was comparatively easy when compared to the Philadelphia sets
The Philly sets were much more harder to find and afford. From 1973 to 1990 the prices were reasonable, but from 1991 to 1998 each set had a price tag of $500.00 or much more - I saw one set for sale at $1200.00. I didn't think that I would EVER get the 1991 to 1998 sets.
But a few days ago, I found a seller that looked like he was dumping his collection, and each set that I needed cost me on average about $160.00 and had every one I needed, so I bought them all

For the Philly Souvenir sets I have from 1973 up to 1998 (minus the 1997 set)
Philly did not have a set for sale 1972, but instead produced a VERY small 'experimental' sets - from whet I found only 5 were created in 1972.
As for the 1997 set, the mint saw diminishing sales on these and only minted 100 sets - So I have a next to zero chance of getting one of them (at least one that I could afford).

In the coming days, I'll be getting them all out and getting them imaged for my records (and to post here to

)

