The antique bullet

"There are indeed grooves, dimples, and other physical design characteristics that are consistent with certain eras and may primarily be associated with particular battles."

No, there aren't. All of the firearms used in WWI had ordinary rifling which can be found in countless types of guns manufactured before and since then. It can be matched to a specific gun if have the specific gun to fire a bullet from in order to make a comparison, but it can't be matched to any particular era (aside from "modern era", which for firearms is from the late 1800s until today).

"I'm recalling a bullet in his collection, for instance, that was never produced in the US and mainly issued during the Crimean War."

There's a big difference between the Crimean War and WWI. Minie balls used in rifled muskets are very distinctive looking, and were relatively short-lived, thus era specific. Even then, if a minie ball were extracted from someone today it wouldn't necessarily be old, because reproductions of both the rifled muskets and the minie balls have existed for a long time, as well as molds for casting your own from molten lead.

On the other hand, WWI was in the modern era. They used metallic cartridges with FMJ bullets in the .30 caliber range and smokeless powder, just as is still commonly used today. The cartridge that the United States military used for example, the .30-06 Springfield, is still one of the most popular rifle cartridges to this day, and one from WWI isn't structurally any different than one made in 1996, or 2018 for that matter.

"Maybe it was a case of the person seeing the lab report and assuming the conclusion because that was what the report indicated."

She was told by a cop. Also, there was nothing which could have possibly indicated that it was fired more than a couple/few days prior, because that's when it effectively was fired.

"I didn't say there was a shape unique to pre - 1930. What I said was the shape (design if you like)and weight of bullets changed after 1930."

But that isn't correct. For military rifle bullets (and their civilian counterparts), spitzers (https://en.wikipedia.org/wiki/Spitzer_(bullet)) in the .30 caliber range have been predominate since the early 1900s, i.e., since before WWI. There have always been a variety of bullet weights used in various cartridges. For example, the standard .30-06 cartridge used by the U.S. military in WWI originally used a 150-grain bullet. In 1925 the standard was changed to a 173-grain bullet. In 1937 they went back to a 150-grain bullet, and have stayed with that ever since. On the civilian market the .30-06 has been available in bullet weights ranging from 110 to 220 grains (and perhaps lighter and heavier than those two extremes), and in the form of a spitzer FMJ, spitzer boattail FMJ, round nose FMJ, spitzer jacketed hollow point, round nose semi-jacketed soft point, spitzer semi-jacketed soft point, and others.

For the sake of argument, let's say the bullet appeared to be from a "Ball, M1906" cartridge, which was made from 1906 until 1925. Keep in mind that there were/are plenty of .30-06 cartridges on the civilian market which use/used copies of the "Ball, M1906" bullet, but let's say that somehow you've conclusively proven that it is from an original "Ball, M1906" cartridge. So what does that prove? Just because a bullet was manufactured a long time ago doesn't mean it was also fired a long time ago. The movie treats it like it's some big mystery that needs explaining; i.e., the cop asks the woman if she wants to change her story, when in reality, the obvious conclusion would just be that Cole was shot recently with an old military surplus cartridge. For example, this guy picked up a box of M1906 ball at a gun show in 2014 - http://forums.thecmp.org/showthread.php?t=147012.

"All refined metals will have different spectrographic signatures due to the source of the ore (or recycled metal sources) and some of the materials used in producing them."

Different spectrographic signatures wouldn't have anything to do with the source of the ore, it would have to do with the final chemical composition of the metal, and it would not establish, nor even suggest, a date of manufacture for a bullet.

"Potash is used to refine lead, potash has trace contaminates of radon, uranium and thorium."

First, that wouldn't help date the bullet, and second (not that it's relevant), where's your proof that potash is inevitably present in the finished refined lead? Also, there are many methods of refining lead. In some cases potash (potassium hydroxide) is used as a drossing agent, but not always. Other drossing agents include coal, ammonium chloride, sodium hydroxide, sulfur, phosphorus, and even air (and that's not an exhaustive list).

"I'd also bet that refining techniques have changed and this would also alter the trace element sigantures."

That's sheer conjecture, unless you can point out a specific refining technique that was never used by anyone in the world after WWI, and how that specific refining technique would "alter the trace element signatures". Also, even if you could do that, it still wouldn't establish a date of manufacture for a bullet, since the dates that the metals are refined and the dates that they are used to manufacture a bullet aren't necessarily the same nor are they necessarily even close together.

"There's also radionuclides which would be missing from a bullet made in 1918 that would possibly be present in a modern round thanks to atmospheric weapons testing in the 1950s that could have contaminated the inputs with cobalt-60."

That's more conjecture.

"The question really isn't whether you can identify it as being not contemporary"

You can't, but feel free to try to prove otherwise by firing a bullet from a WWI surplus cartridge into a carcass, and then see if there's any lab in the world that can conclusively establish when it was manufactured.