Fourthgeneration -
Where are you and what standards are in effect?
Take a look at ACI 530 (Design and Specifications for Masonry Structures). It is the bible for masony in the U.S. and many foreign countries. It is published by ACI since they have the systems and means to distribute document. The document is written jointly by the MJSC (Masonry Joint Standards Committee), TMS (The Masonry Society) that has member that are contractors, engineers unions, material suppliers, state and national associations and educators, the NCMA (National Concrete Masonry Association that is comprised for material manufacturers and sellers), the BIA (brick manufacturers and distributers), masonry contractors and few others. These groups also are respondible for the the ASTM standards for specification of material standards, test and sampling methods and reporting. It is a very valuable that addresses masonry design and construction in a good format with some tables, drawings.
I am not aware of any place where a one block with grouted cores is acceptible unless it is in a location with unique standards or spec writers with strange ideas. The commonly used site sampling and preparation of site is a 4"x4"x8" cube that is form when 4 block are laid to make a 4"x4" square to be filled with grout after some absorptive paper lines the cavity. This allows the block to absorb the excess moisture as it sets and cures and is truely indicative of the properties of the grout in place and the block are not adhered to the sample that can be removed after the block are removed. - A core of a single block is irregular, impossible to measure and cannot be removed, so the block will affect the test. As you know, the cores of the block are not square and the widthe of the core varies since the block have tapered cores and the top may have a flaired face shell and webs for the convenience of contractors. - There is a similar test for grout in brick construction, where the brick are stacked in a similar pattern.
Regarding ASTM standards, there many individual volumes on different related subject. There is one for mortar that also gives the standards of the components and the products themselves. The individual standards (ASTM C90 for concrete masonry units as an example) and others are revised when needed to keep current with others referenced in it. The volumes are reprinted very often and contain all the current standards whether they are changed or not for convenience. - I only really reference one volume for my purposes. Since, I am a member of ASTM ($75.00/year), I get a free volume of my choice annually (hard copy or on line in detail), so that is a great bargain and the $250 does not sound right. As a member, I can download any standard in the volume I choose and print it and use as I choose. Since I am a member, I can go to the site and reference any standard in any volume and buy it at a greatly reduced member price (not need to buy the entire volume of the set of about 30 volumes. - Take a look and you be surprised at what is available for $75 per year that is a business expense deduction.
Again, the "mortar" test you referred to does NOT test the strength of the mortar, but the strength of the mortar and block together. The compressive strength of mortar is not important in the strength of masonry since you can make a 2 block face shell bedded prism out of high strength block and 2000 psi mortar that tests almost 5000 psi, since the masonry unit strength governs. - This is all shown and explained in the ACI 530 I mentioned earlier.