One can tell a real tan Lavirus from a Wonderbread Lavirus.  The difference is in the shape of the die-cut around the lid of the bottle (see the picture).  The regular one (white or tan) is more rounded, the wonderbread's die-cut has corners1.  What's more, one can tell these Laviruses from a Lavirus coming from a 1979 Test Pack (test packs contain a mix of 1st and 2nd series white backs).  The test pack Lavirus's die-cut is more square than the original, but the corners are rounded off, unlike the wonderbread's.  One might expect the test pack Lavirus's die-cut to be the same as the regular 1979 rerun Lavirus (series 2), but that's not the case.  The test pack Lavirus has its own unique die-cut shape.  In fact all test pack stickers seem to have unique die-cuts different from the originals.  So conceivably one could collect an entire run of test pack stickers.  That should keep anyone busy.  Test packs must have been pretty popular, because Topps followed them with four series of bonafide reruns, so maybe there are a fair number of them floating around.  From the known test-pack stickers, it appears they are exactly the same titles as on the 2nd mail in wall poster, so 33 titles from the 1st and 2nd series.
1. I believe this was first noticed by Ed Glicken, and passed on to the community at the 1998 Chicago non-sports show.
Return to the Wacky Pack Homepage