A.
Your interpretations of 1) and 2) do not spell out to the details however they are generally correct. Your interpretation of 3) is totally incorrect. Without any exception, liquid substance with a vapor inhalation toxicity is totally forbidden for air transport even if the quantity per package is reduced to less than 5L. There is no exception. They are absolutely forbidden.

For your reference, below shown is the full text of SP A4.

“SP A4 Liquids having a vapour inhalation of Packing Group I are forbidden on both passenger and cargo aircraft. Liquids having a mist inhalation toxicity of Packing Group I are forbidden on passenger aircraft. They may be carried on cargo aircraft providing they are packed in accordance with the packing instructions for the Packing Group I substance and the maximum net quantity per package does not exceed 5L.

Transport in accordance with this special provision must be noted on the Shipper’s Declaration. When transported in accordance with this special provision and packed with other dangerous goods in one outer packagings, the maximum quantity per package used to calculate the Q value for this entry must be the net quantity specified in this special provision.”