There are many owners, sellers, flippers, etal out there claiming "1-of-some number" for their car. Many of which are misunderstandings, misconceptions, and most (sadly) just plain lies. Claims like "1 of 6 black SS 396 convertible with 4-speed" are, at best, misleading and not true.
While one can determine how many of a single option was sold, there is no way to know just what that option was installed on in most cases. There are some exceptions, yes. We'll use the 1970 model year for the following since this is a very popular model year.
It is known, for example, there were 7,522 1970 convertibles built, 381 with the 25ocid L6 and 7,141 with some V8. Since there were a number of V8 engines available (the 307, the L48 350-2, the L65 350-4, the LS3, the L34, the L78, the LS5, and the LS6), one can only calculate an even distribution of those 8 different V8 engines.
One can, correctly, determine how many of certain options were sold by simple math. For example, the SS396 option came wiht the base L34 engine or an optional L78 engine. Since the L34 engine was not an option as such, one can subtract the number of L78 engine options (2,144) from the total SS396 options (53,599) to determine that 51,455 SS396 Chevelles have the base L34 engine. Same for the SS454 option. The base LS5 engine is not an option as such but by subtracting the number of optional LS6 engines (4,475) fro the total SS454 options (8,773) to determine that 4,298 SS454 Chevelles have the base LS5 engine.
If one wants to know how many ZL2 options were sold, that's easy as production reports puts that number at 28,888. This number represents to total number of ZL2 options sold but here's the catch, the option does not tell you how many were sold on sport coupes, convertibles, or El Caminos. Once can calculate an even distribution but that's all. First one has to determine how many Malibu convertibles, sport coupes, and El Caminos were built then determine the percentage of each model against the total. The image below shows these calculations. Convertibles made up 2.12% of the 3 different body styles that could order the ZL2 hood, sport coupes made up 85.82% and El Caminos made up 12.07%. Assuming an even distribution you get the numbers shown.
One can do a similar calculation on how many ZL2 options were sold by one of the 4 possible SS optioned engines. For example the L34 engined SS396 makes up 82.50% of the 4 engines possible in both SS options. By taking 82.50% of all the ZL2 options, one gets 23,833 ZL2 options sold with the base SS396 engine. A fact? No, just an even distribution.
Now what happens when you try to determine how many L34 and ZL2 options were sold in convertibles? You cannot do it. First you can only determine how many SS396 convertibles were built by percentages and there's no way to even calculate how many of those may have also ordered the ZL2 hood.
The same fallacies of numbers continue for any option that could be ordered on more than one body style, with more than one engine, etc. such as D88 Hood & Deck Stripes, TH400 automatic transmissions, even bucket seats.
So the next time you see a poster claiming there are 18 454 LS5 convertibles with a TH400 and ZL2 hood or hear a seller claim their black SS396 with A/C and red bucket seats is 1-of-10, remember this page.