Bullion Coins From The 70's?

But pre-1964 US coins have NOT continued until this day in 90+% silver.
Also, bullion coins typically have an explicit statement of weight (or mass) and fineness on the coin which the pre-1964 US coins do not have.

In the early 1970s silver was still in general circulation in many countries, and people hoarding silver just took coins from change. There were gold bullion coins available: the Krugerrand had been struck since the 1960s and the British sovereign was generally considered a bullion coin.

South Africa were the pioneers in the "bullion coin" concept. You can tell that krugerrands were "early concept", because they retained a key component of circulating gold coins: they were .900 fine, rather than .999. The Mexican Libertad is another early example of a gold bullion coin. And krugerrands and Mexican onzas are unique in not having a fixed legal tender "denomination", per se, but being "denominated" in troy ounces, and their legal tender value fixed to the London spot price of gold.

The krugerrand was launched in 1967, the onza in 1981.

The only other "early bullion coin" not yet mentioned was the Austrian 100 corona dated 1915, which is still being struck bearing that date. More like a "restrike trade coin" than a proper "bullion coin" - kind of like the gold equivalent of the Maria Theresa Thaler. However, it too was issued in .900 fine gold, and to an odd amount of almost, but not quite, 1 troy ounce of fine gold (0.9802 ounces, or just slightly more than a USA double-eagle).

The "silver bullion coin" was much slower to take off; it was considered too cheap and bulky to be worth stacking, compared to gold. And there were still plenty of old silver coins to be found, for those of the minority who did want to store silver coin. I think here the Mexicans were first, with their silver Libertad in 1982.

Fair enough, but there was a hiatus between 1964 and 1992.
Also, these coins do not have an explicit statement of weight (or mass) and fineness on the coin.

Historically, Spanish cobs and 8R's, and the Trade dollars, filled a role as silver bullion. They did function as currency to some extent, but they were more useful in trade for their metal content than any stated denomination.