The oldest PCGS slabs are also called "rattler" slabs with what looks like typewriter printing. They then had the green slabs with better printing and sometimes called OGH, (old green holder). Next you have the blue slab and now you have the blue slab that also will show edges.
the first generation PCGS has a green label and the holder is small and the coin rattles around in the slab, these are called rattlers. The next generation holders also had a green label but was the same sized holders they use today. about 10 or 15 years ago everyone would be hunting fore these older slabs because their grading standards has become more lax since then and they thought they would get an upgrade. Now most of the coins that would have upgraded have already been sent in for an upgrade and this is no longer the case. You do get a few people that still look for these old green labeled holders and they sometimes pay a premium for them but chances of any of them being upgraded are very slim as their grading standards have changed a few times throughout the years and the ones that were really undergraded have been sent in already