Well there may be others who know more about sample slabs, but to my knowledge they are still making them today. Pretty sure there are a lot more than one might think.
Some are very rare (i.e. only 1 or a few known) while others are very common (hundreds). The grading companies should know how many are produced, but that info usually isn’t made public. @Davidschwager has written the book on these and you can learn about relative scarcity there. Also you can always post a picture of your example and the sample experts on here will help you learn more about your slab.
Some are labelled 1 of 160 or such. Some cert#s are reused - 199998-xxx from NGC was used many times. Per the database, there are 25 Liberty V Nickels (Schwager# NGC-005-4-1) but I've been tracking these for several years and can document at least 8 uses, or almost 200 total. Most are total mysteries...
You can get sample slabs at major coin shows like ANA. My daughters did the questionnaire and they gave them dollar coin samples.
