As far as I know there is no shortage of fossilized/opalized palm wood. The difference is simply a matter of when they were made. I'm not an expert so wait for some of the more educated folks to chime in.
There are several past posts about pumtek beads that discuss these issues. Did you try a search?
Old Versus New
When pumtek beads appeared in the marketplace in 1983, they were immediately compared to Tibetan zi beads and presumed to be ancient. Having pursued some preliminary research at the UC Berkeley library I (nearly immediately) attempted to counter this idea of great age. In 1986, consulting with Lois Dubin, I urged her to place these beads in her Bead Chart in modern times (not thousands of years ago). I said "I don't believe these beads are more than 300 years old, as a gut feeling, and based on what I have read." We agreed to place them in the 17th C., and not in antiquity. Some years later, it was determined that they actually date from the 1920s—and this will be reflected by their placement in the new Bead Chart in the coming revised edition of The History of Beads (in October).
The value of pumtek beads has already lowered and raised twice. The first strands were expensive (due to no real knowledge nor familiarity with these beads, and the look-alike association with Tibetan beads, already mentioned). In a short time, strands and traditional necklaces were plentiful, and prices went down. This was concurrent with a plethora of Indian tribal jewelry—particularly Naga and Hill Tribe pieces, that were commonplace and, for a while, were abundant and inexpensive (from ca. 1982 to 1992.) Once the supply dwindled, the costs of these beads went up again. Of course, patterns and shapes that were deemed to be "rare" always cost more at any time. However, as soon as new editions began to circulate (also the early '90s), and when they became technically good, prices went down again. (This always happens when collectors are no longer confident they can distinguish between authentic early beads and later editions; and when the new copies are decent and inexpensive.) Also, the fad for acquiring them ended, for most intents and purposes. Now, many, many collectors know rather little about pumtek beads, despite my considerable interest, publishing two articles, the publications of other authors, and the nature of the marketplace. (They are still routinely thought to be much older than they are—partly because of their relationship to ancient Pyu/Mon beads.)
Pumtek beads are hardly "worthless." But they have undergone the flux in pricing I have just described.
Composition and Manufacture
Pumtek beads are (in the main) composed from fossil palmwood, that is a variety of non-precious opal (unlike many fossil woods that have become agatized). It is correct to say they are "fossil wood," "fossil palmwood," opalized wood," and "petrified wood." The opalization of palmwood (or any wood) is a petrification (though it is different from agatization). This is not complicated stuff. The problem lies, in part, with the suggestion that not ALL pumtek beads derive from palmwood. It has been suggested by a mineralogist friend of mine that other fossil wood has been used as well in the manufacture of some pumtek beads. (I don't have a second opinion on this, yet.)
One seller of new pumtek beads has forcefully said that the new beads are not fossil palm wood. I entirely disagree! In my opinion the material is the same—although there are specimens that have "plain" (unpatterned and undecorated) areas that do not feature the grain of palm wood. This is opal that filled-in cracks in the palmwood. I can show specimens of the raw (or rough) material—and I have specimens of fossil palm wood collected by my friend Mark Kenoyer in Nagaland in the 1950s, that he gave me quite a few years ago. (I was the first one to show him pumtek beads in 1984.)
Throughout the 1990s and into our present century, in Burma, new editions of pumtek beads have been made. The earliest of these probably date from the very late 1980s. Over these years, these new editions have tended to become more and more like the early pumtek beads, in terms of sizes and shapes, and the technical facility of their patterning. (Meaning the beads are nicely colored brown or black, and feature strong white lines, or the reverse. They are not ashen like the first reproductions/editions of the late '80s, nor pale and patchy.) About seven years ago, the current editions of pumtek beads were excellent in quality, and most-resemble the prototypes of the '20s—apart from looking new, and the designs, that gradually became a combination of old and new/different patterns—as I showed recently here. I have collected specimens of all of this production throughout the past twenty-six years. I have original necklaces, bags of loose beads, necklaces I made from the best beads, new necklaces, and new specimens.
It has been said that production stopped due to government intervention ("forever") about four or five years ago. Consequently, the beads I bought at Santa Fe a month ago are from about five to seven years ago. For all we know, the manufacture continues surreptitiously (or even openly)..., or might be revived at any time. "Forever" is a long time to speculate about....
The article that I composed, posted here, actually shows more than just "a sketch of a necklace." Above it is a color photograph I took in about 1984 or '85 of eight typical beads. But this is not an article about pumtek beads—so there was no need to show more.