12 Tops: the (one and only?) end-of-year compilation

Discoveries in the world of 12 Tops, so far as the tape editions are concerned, have been fairly numerous this month. Recent blog posts include a copy of 12 Tops volume 1 on cassette, as well as an alternative edition of volume 19 on 8-track. Now, another find, also on 8-track - the alternative edition of the only (so far as I know) end-of-year collection from the series, Top 20 1973.

As seems standard across the 12 Tops cartridges, this is known is both green and white shells. Both came out in identical slip cases. Here are the scans, firstly of the slip case:

And the cartridges themselves. They appear identical in all respects, except for the colour of the plastic. It's not clear why both green and white editions were made:  

As noted, this album is probably the only case of the 12 Tops series being compiled in this way, and no vinyl edition is known. The contents reveal that the cartridge was probably issued some time before the close of 1973, since the final two albums of that year are not sampled on the collection. What we do have is two or three tracks from all the other 1973 LPs - volumes 8 to 15 inclusive. Wouldn't it be amazing if an LP edition turned up? Nothing would surprise me any more!