Apple iTunes Music Purchases

Many of my purchased songs in the Apple Store do not show as purchased when I go back into the store and browse the album it was purchased from. As an example, I bought the song "Love in Vain" and three other tracks off the Rolling Stones LP "Let it Bleed". When I go into the store now and look at the album, the option is to buy those songs. It does not show "play" nor does it show that I can complete the album for a reduced cost since I have already bought 4 tracks. This is the case for most all of my older purchases from 2006 through 2012 and it also is hit and miss for purchases from 2013 and later. The songs are in my iTunes Store account purchase history. Any suggestions as to why certain song purchases do not show as already purchased in the Store?