A lot of the bloody decks *themselves* are not acid-free - you've got to have grave suspicions of the cardstock chosen by people who would laminate them without even hesitating <grin>.
I am a Collector of Books, born into a family who were Collectors of Books for generations before me.
As such, one of my proudest possessions is a very, very fake replica of a Shakespeare First Folio, printed in 1850. It was printed on the cheapest paper available at the time, and bound in the cheapest covers of the time - leather. Over the years, it has had mice nibble at the edges of the pages, and quite probably sustained silverfish attacks (it has never been stored other than on domestic shelving, and has had no restorative work done). When you open it now, it opens easily, and the el-cheapo paper of the pages is white and flexible, turning easily. The print is clear.
In the late 1970s and early1980s was my BIG book-buying period, many a week. Then, the idea of "washing" paper in acid baths at the point of manufacture before the publishers ever bought it, was just becoming standard for paper manufacturers, so that any individual fibres that may be differently-coloured to the rest of the woodpulp would blend in and the sheets of paper would be a pure, dazzling white instead of almost-white. As a result, I probably have between 900 and 1,250 books (I'm not going to physically count them) which were acid-washed from that era. By the time the late 1990s rocked around, the pages had browned exactly as if they'd been held too close to a fire, and started becoming brittle: bits of pages have broken off the edges of pages as I've turned them before now. I have whole areas of literature that I'd love to re-read that I don't dare open, and they were largely written before wordprocessors became widespread and nearly all before the internet became a widely-used tool, so when the last copy disintegrates through acid-burn, those books will be lost to the world forever.
My 1850 "First Folio", aside from the ravages of vermin, are as good as the day they rolled off the press, long before the advent of acid baths.
Artists have to be careful about buying acid-free paper for essentially similar reasons, and we have no way of checking whether Tarot decks are printed on acid-free stock. My thinking is that if they were, it's be mentioned (it always is with other paper products) so if there isn't a mention of acid-free stock, then probably given a couple of decades the cards will start to scorch themselves from the inside.
<sigh>
