No, the multiple third party grading companies do not exchange information.
The best way to look at the pop reports is to imagine them as a list of production runs. The number is basically how many times they graded a particular card. They graded card "X" 25 times...wether it was the same exact card 25 times or 25 different copies of the card no one knows. The only thing you do know is there is a maximum amount of 25 graded examples.
Even though all the population reports are majorly flawed and there is nothing the companies can do about that, the most important thing to remember is that the number you are looking at will always be the maximum number of copies available. There will never be 10 copies of a Pop 5 card but they most certainly may be only 5 copies of a Pop 10 card.
Ford can tell you how many Mustangs they made in 1970 but they can't tell you how many still exist.
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